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Hypothesis #8

Reproduction

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Sam keeps sleepwalking . . . and waking up in the wrong bed.

Samantha Jarlston keeps telling herself she doesn’t want to get romantically involved with her former childhood best friend and current partner in crime, the very sexy chess grandmaster, Andreas Kristiansen. But despite her many, many, MANY protestations, Sam keeps waking up in Andreas’s bed. Even worse, he’s adorably flustered and shy about it. Every. Single. Time.

Sleepwalking into Andreas’s bedroom and his cute reactions aren’t complications Sam has time for, not when she needs to get back on track with her Ph.D., catch up with her part-time job while avoiding the inappropriate Dr. James Nieminen, not to mention juggling the demands of exacting revenge on the Kristiansens.

Basically, her social calendar is quite full.

Does her subconscious know something her conscious brain does not? Is Sam ready to give up on revenge once and for all and figure out how to make things work with her first love?

And what happens when Sam finally discovers adorable Andreas’s dirty little secret?

‘REPRODUCTION’ is book 2 in the ‘Fundamentals of Biology’ trilogy, ends on a cliffhanger, and cannot be read as a standalone. ‘Fundamentals of Biology’ is the third trilogy in a series of trilogies that begins with ‘Elements of Chemistry’ and ‘Laws of Physics.’ You do NOT need to read ‘Elements of Chemistry’ or ‘Laws of Physics’ before reading ‘Fundamentals of Biology.’

Paperback

First published October 16, 2025

215 people are currently reading
7237 people want to read

About the author

Penny Reid

92 books22.5k followers
Sign up for the newsletter of awesome: www.pennyreid.ninja/newsletter

Penny Reid is the New York Times, Wall Street Journal, and USA Today bestselling author of the Winston Brothers and Knitting in the City series. She used to spend her days writing federal grant proposals as a biomedical researcher, but now she writes kissing books. Penny is an obsessive knitter and manages the #OwnVoices-focused mentorship incubator / publishing imprint, Smartypants Romance. She lives in Seattle Washington with her husband, three kids, and dog named Hazel.

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5 stars
520 (44%)
4 stars
421 (36%)
3 stars
189 (16%)
2 stars
23 (1%)
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5 (<1%)
Displaying 1 - 30 of 97 reviews
Profile Image for Penny Reid.
Author 92 books22.5k followers
Want to read
October 16, 2025


NOW AVAILABLE
This is not a drill, the wait is finally over! REPRODUCTION is available on all platforms! Go forth and read the nerdy goodness!
 
Tropes
Fake Dating
Plot with multiple twists
Women in STEM
She's morally grey
He's morally grey too...
Forced Proximity
Former childhood friends to lovers
 
Read Book 2 REPRODUCTION now: https://geni.us/ReproductionPR
Read Book 1 INHERITANCE now: https://geni.us/InheritancePR
Pre-Order Book 3 EVOLUTION: https://geni.us/EvolutionPR

**Blurb**
Sam keeps sleepwalking . . . and waking up in the wrong bed.

Samantha Jarlston keeps telling herself she doesn’t want to get romantically involved with her former childhood best friend and current partner in crime, the very sexy chess grandmaster, Andreas Kristiansen. But despite her many, many, MANY protestations, Sam keeps waking up in Andreas’s bed. Even worse, he’s adorably flustered and shy about it. Every. Single. Time.

Sleepwalking into Andreas’s bedroom and his cute reactions aren’t complications Sam has time for, not when she needs to get back on track with her Ph.D., catch up with her part-time job while avoiding the inappropriate Dr. James Nieminen, not to mention juggling the demands of exacting revenge on the Kristiansens.

Basically, her social calendar is quite full.

Does her subconscious know something her conscious brain does not? Is Sam ready to give up on revenge once and for all and figure out how to make things work with her first love?

And what happens when Sam finally discovers adorable Andreas’s dirty little secret?

‘REPRODUCTION’ is book 2 in the ‘Fundamentals of Biology’ trilogy, ends on a cliffhanger, and cannot be read as a standalone. ‘Fundamentals of Biology’ is the third trilogy in a series of trilogies that begins with ‘Elements of Chemistry’ and ‘Laws of Physics.’ You do NOT need to read ‘Elements of Chemistry’ or ‘Laws of Physics’ before reading ‘Fundamentals of Biology.
Profile Image for Inguna.
182 reviews1 follower
October 17, 2025
The second book leaned even more into Samantha’s quirks. Still no real growth in her—except that she finally started taking showers. Yeah.

For most of the book, it felt dragged out. Their endless back-and-forth about what was fake and what wasn’t left me with too many eye rolls. I might have been more patient if they were high schoolers, but she’s supposed to be 28, in STEM, and all that. I started skipping parts like: oh, he held my hand, what should I do and what does it mean? Or we woke up together, he had his morning… situation, and he looked at my mouth—must be my bad breath.

Finally, we got to the conflict at the end. To me, it felt too Penny Reid. Andreas got something from their deal that Samantha didn’t know about. So what?

Now I’m left with a dilemma—is it really worth paying another 5–6 EUR for the final 200 pages? I’m just starting to feel used.
Profile Image for alana ☁️.
1,171 reviews1,353 followers
December 29, 2025
I have some feelings... and they better be addressed in the next book. because if they aren’t.... I’m going to be seriously disappointed. dear Penny, I’m talking DISAPPOINTED.
Profile Image for Nicole Namen.
381 reviews10 followers
October 20, 2025
Super good!!! Exactly what I wanted!

Ooooof, this book killed me! I loved it so much. I love Andreas and Sam so much. But Andreas did Sam so dirty in the end, why not just tell her the truth so she wouldn’t get hurt. Yikes. So cold. Now it’s time for him to grovel because he has a lot to make up for. I don’t know how he will do it but I’m excited to see. This book was so so good. It’s exactly what I wanted to read and I can’t wait for the rest of their story! Sam deserves so much better and he has to do better for her. I hope Sam doesn’t go back to her old reclusive ways. I can’t wait to find out! Love this book and this series so much!
Profile Image for Krista.
1,136 reviews66 followers
October 17, 2025
Book 2 picks up right where the first left off—and I was hooked from the very first page. I devoured it in a single day. I even woke up at 3 a.m. replaying scenes in my head, analyzing every interaction between Sam and Andreas like I was the main character, hunting for clues I might have missed. That’s how immersive this book is.

The twist this story takes? I did not see it coming—and I loved that. It kept me on edge, flipping pages with an urgency I haven’t felt in a while. The emotional pull and the intense attraction between Sam and Andreas were off the charts. Their chemistry? Absolutely electric—it smoked.

What I really appreciated was how the book balanced steam, suspense, and humor without losing the emotional depth. Sam is juggling so much: academic pressure, shady coworkers, revenge plots, and the infuriatingly sweet and sexy Andreas—who somehow manages to be both confident and adorably flustered. Watching her try to make sense of her sleepwalking (and waking up in the wrong bed... repeatedly) added such a clever, playful element to the romance.

And yes—this book ends on a cliffhanger. A brutal one. I will be impatiently awaiting Book 3 because I need to know what happens next.

If you love smart, spicy romance with mystery, slow-burn tension, and unforgettable characters, don’t miss this one. Just make sure you clear your schedule—you won’t want to put it down.
Profile Image for Em (semi-hiatus).
750 reviews278 followers
November 29, 2025
Lovely characters, zero spark. Their romance had all the charm of two strangers politely holding a door open for each other. That plot twist at the end, though, actually got me.
Profile Image for Cassandra Martin.
924 reviews58 followers
October 16, 2025
Going into this one I KNEW there was going to be a rough cliffhanger, and now I have to wait three weeks to find out what happens next?!

General thoughts on this one:
• Spice (ALL THE SPICE!!)
• Andreas really started to remind me of Quinn in this book (will discuss with other Sharks once they have read)
• There was one twist I seriously did not see coming
• I’m really enjoying the Andreas chapters at the end of each story, the longing, the guilt. His backstory is very interesting!

Can’t wait for Nov 6th!
26 reviews
October 22, 2025
Wow

This book was better than the first one. I didn't see this plot twist. I can't wait to read the next book!
Profile Image for Ruby.
5 reviews2 followers
October 18, 2025
This just isn’t working for me
Profile Image for Rita.
364 reviews8 followers
October 20, 2025
One of my favourite OG authors - I’ll read and enjoy anything she writes.

And yet, I despise when what should be one book is split into several and we have to wait weeks for the next part 😭

I guess I’ll see you in three weeks, PR 👑
Profile Image for Elle ♡ [semi-hiatus].
765 reviews113 followers
November 29, 2025
*slight spoilers* Penny Reid’s obsession with mid twenties+ male virgins strikes again 🫡 idk why I wasn’t expecting it, but duh. Anyway, this book was alright. It was obvious Andreas has some secret he’s holding back leading to an annoying miscommunication trope where they’re both so obviously in love with each other and misinterpreting everything and blah blah blah. The end was kind of interesting, I don’t feel like his secret had to be a secret. Samantha wouldn’t have cared, it might have even made her more willing so it kinda just pissed me off, but I also don’t think it’s a big deal lol. I am a bit surprised by Andreas’ POV (only last chapter of course even tho PR labeled each chapter as Samantha’s even tho duh that’s the default just let me know when it changes…) and how he’s been feeling this whole time/his initial motivations. Yeah, honestly a bit shocking. I will be reading the last book but I don’t love this series 🧐
Profile Image for Maliha.
116 reviews11 followers
November 11, 2025
i want to high five Andreas. with a chair.

man i didn't expect it in the end. can't say i wasn't happy when one upped his brothers lol.
5 reviews
November 11, 2025
It’s a good thing the sequels are released close together or I’d have to wait to read them all together! Just enough time in between to anticipate how this great story and relationships are going to resolve!
Loved this 2nd book of the trilogy! I was not expecting that ending and I’m rarely surprised these days. Love both main characters and can’t wait to see their HEA!
Profile Image for Marian.
25 reviews5 followers
October 20, 2025
So smart…and exasperating!

The story continues, like a roller coaster with bunny hills that make your stomach lurch and roil. It was over so fast and has left me wondering how to get through the next couple of weeks without knowing what will happen. Why do I let this happen to myself??
1,099 reviews3 followers
October 25, 2025
Gah, why did Reid split these books into 3?!? If book one was all about the sexual tension and slow burn, book two is the explosion of that tension. Andreas and Sam finally give into that tension and wow, is she a lucky lady. The two continue to present themselves as the in-love engaged couple. You can tell, however, that feelings are growing for both of them. But then something unexpected happens and the chess game strategy comes more into view. This one ends on a sad note and leaving me with a feeling of desperation. With the intelligent humour expected from Penny Reid, Reproduction also brings the feels. As I anxiously await the finally of this series, giving this one 4.5 stars.
Profile Image for kappa_79.
192 reviews
January 19, 2026
Great part 2. Ends with a heartbreaking truth. Definitely need to start part 3.
Profile Image for Jenn Brown.
7 reviews
January 26, 2026
Even better than the first. Crushing my spirit that I have to wait for the 3rd book to come in at the library.
Profile Image for Rachel.
279 reviews4 followers
January 31, 2026
Thank you for the little twists 💁🏻‍♀️
Profile Image for Nomims.
1,799 reviews12 followers
November 28, 2025
3.75 stars

The back and forth in this one was a bit frustrating lol but this one was really about them slowly getting together and they were sweet. I didn't understand Andreas at all though. I kinda guessed he was suss a bit but his reactions still didn't made sense. The ending was of course dramatic but kinda expected.
431 reviews1 follower
October 25, 2025
Classic Penny Reid, especially after consuming Elements of Chemistry series. The plot thickened in this 2nd of three books. Very engaging and I wasn't surprised by Andreas's status prior to Samantha's decision to change the nature of their relationship. However, I didn't agree with how she made the decision to advance their relationship into something more involved. That seemed a little callous to me.
Really interested in the direction of book 3.
Profile Image for Nicole.
74 reviews1 follower
October 20, 2025
This is so juvenile. They are not in high school.
Profile Image for Nicole.
224 reviews9 followers
January 3, 2026
I wrote one review for the series and am posting it for all three. Don't hate me, I'm being efficient, and in the wise words of the Doctor... no spoilers.

✦Series: Hypothesis, 7-9 • ♟️Fundamentals of Biology 1-3♟️
MF romcom with a heavy dose of suspense. The return of the Hypothesis series is smart, twisty, funny, and completely bingeable. I devoured the trilogy in two days.

1️⃣ Inheritance
Andreas approaches Samantha with an unconventional way to take back her birthright and restore her late parents’ reputations.

2️⃣ Reproduction
Their fake engagement doesn’t feel so fake once they move in together to make it look real; they’ve been crushing on each other since they were kids. It doesn’t help that Sam keeps sleepwalking into Andreas’ bed. Hello, one bed!

Aside: the twist at the end of this one made me want to scream. Well done, Penny! I did not see that coming.

3️⃣ Evolution
Sam will take back what should always have been hers with or without Andreas, but Andreas has no intention of letting her go.

Here’s where it goes wild with drama and suspense. It’s thrilling, and the way Penny weaves the subplots together is straight-up wizardry.

✦POV: Single, first-person
The books are told in Sam’s POV with Andreas as the last chapter in books 1+2. This was a brilliant idea. Understanding his struggles in the moment cranked the drama and kept me obsessively reading.

Sam is a STEM PhD candidate. She’s strong, funny, clever, and relatable. I loved reading her thoughts and how she navigated what the story threw at her.

Andreas is a young, billionaire, chess grandmaster who earned fame because he’s undefeated and wields stoicism like a weapon. His character arc was so unexpected! His hopeless devotion to Sam is tender and swoony.

✦Spice: Open door, explicit
It’s a slooow burn, but it is worth every page to get there. The tension is achingly delicious. 😮‍💨🫠

♡ Eloquent, funny, clever- Penny’s books lock me in, I’m hooked every time. The stories her mind conjures are a gift! Enjoy with confidence. 👏

⚠️ Please check trigger warnings!

✨ Enjoyed thanks to Toronto Public Library and Libby.

⭐️⭐️⭐️⭐️½ rounded up!

→ Connect with me on Instagram!
Profile Image for Nicole.
224 reviews9 followers
January 12, 2026
I wrote one review for the series and am posting it for all three. Don't hate me, I'm being efficient, and in the wise words of the Doctor... no spoilers.

✦Series: Hypothesis, 7-9 • ♟️Fundamentals of Biology 1-3♟️
MF romcom with a heavy dose of suspense. The return of the Hypothesis series is smart, twisty, funny, and completely bingeable. I devoured the trilogy in two days.

1️⃣ Inheritance
Andreas approaches Samantha with an unconventional way to take back her birthright and restore her late parents’ reputations.

2️⃣ Reproduction
Their fake engagement doesn’t feel so fake once they move in together to make it look real; they’ve been crushing on each other since they were kids. It doesn’t help that Sam keeps sleepwalking into Andreas’ bed. Hello, one bed!

Aside: the twist at the end of this one made me want to scream. Well done, Penny! I did not see that coming.

3️⃣ Evolution
Sam will take back what should always have been hers with or without Andreas, but Andreas has no intention of letting her go.

Here’s where it goes wild with drama and suspense. It’s thrilling, and the way Penny weaves the subplots together is straight-up wizardry.

✦POV: Single, first-person
The books are told in Sam’s POV with Andreas as the last chapter in books 1+2. This was a brilliant idea. Understanding his struggles in the moment cranked the drama and kept me obsessively reading.

Sam is a STEM PhD candidate. She’s strong, funny, clever, and relatable. I loved reading her thoughts and how she navigated what the story threw at her.

Andreas is a young, billionaire, chess grandmaster who earned fame because he’s undefeated and wields stoicism like a weapon. His character arc was so unexpected! His hopeless devotion to Sam is tender and swoony.

✦Spice: Open door, explicit
It’s a slooow burn, but it is worth every page to get there. The tension is achingly delicious. 😮‍💨🫠

♡ Eloquent, funny, clever- Penny’s books lock me in, I’m hooked every time. The stories her mind conjures are a gift! Enjoy with confidence. 👏

⚠️ Please check trigger warnings!

✨ Enjoyed thanks to Toronto Public Library and Libby.

⭐️⭐️⭐️⭐️½ rounded up!

→ Connect with me on Instagram!
Profile Image for Marjorie.
624 reviews
November 13, 2025
Book Review: Reproduction (Book 2)
Rating: 3.5/5 Stars
​We are back with Book 2, where the farce continues. Sam and Andreas are living together and selling the image of a happily engaged couple to the public. But the engagement is just a smokescreen for their actual, legally binding maneuver: Andreas is adopting Sam as his legal daughter so she can inherit shares of his father’s company. ​Naturally, because this is a romance novel, they are also harboring massive crushes on each other.

​I was thoroughly devouring this book right up until the final stretch. The pacing was solid and the banter worked, but that ending pulled me right out of the immersion. The "big realization" wasn't surprising, nor was it malicious enough to warrant the nuclear reaction from Sam. The explanation was there, but logically, it didn't track. The outcome seemed perfectly fair. No one lost. No one was irreparably harmed. And didn't Andreas deserve to keep all of his mother's things? What's so bad about his keeping his dad's physical assets? Why the fury? I'd have been happy he got to keep things after being tortured by his family his whole life. ​I can understand being annoyed that information was withheld. Sure. I get that. But generating a dramatic Third Act Breakup over a reveal that ultimately benefited everyone feels forced. The conflict in Book 1 was arguably worse, yet it played second fiddle to this manufactured outrage.
​I am less excited for Book 3 now, mostly because I assume the characters will eventually arrive at said logical conclusion, and just kiss and make up.

​But seriously, even with that out of the way, we need to address the elephant in the room. How do you explain to people that you are dating your legal daughter/father? If you cancel the adoption, the entire plot is defeated. I guess we'll see.
Profile Image for Donna.
1,443 reviews13 followers
October 18, 2025
Andreas & Samantha ❤️

🧬When PhD student Samantha receives an thick invite in the mail to her own wedding, she’s more than surprised. The groom is Andreas, the boy who she adored as a child, until everything turned sour.

🧬When Andreas suggests marriage to find a way to circumvent his father’s inheritance wishes, she knows she can’t do it. But an adult adoption could work. Coupled with a fake engagement that will put his evil brothers off the scent may just work.

✏️I am at the point where I have read everything Penny Reid has written, and if she writes it, I am guaranteed to love it. This story is a serial in three parts. I made the mistake of starting to read Inheritance when Reproduction was just released, and now have to be patient for Evolution to come out. The cliffhangers are working; I can’t wait to see how things will work out for the brilliant chess grand master and the lovely scientist who’s captivated his heart for so many years.

Read on Kindle
My rating 5/5 - ⭐️ ⭐️ ⭐️ ⭐️ ⭐️

Connect with me: http://www.instagram.com/read.athon2021


Profile Image for Vr.
216 reviews1 follower
October 29, 2025
I absolutely adored this second instalment and can’t wait for the third! What I love about Penny's writing is how her main characters express their love through actions rather than just words. The way she crafted certain scenes, like the first date with all of Sam's friends and the breakfast moments, made Andreas's feelings for Sam incredibly clear. I truly enjoyed the writing, but Sam's reticence sometimes left me a little frustrated. When Andreas said Sam should not want to be with him, my heart sank. From that point forward, though, the book felt like a cosy read with a warm cup of tea on a rainy day.
However, the ending was quite unexpected. I found myself liking Andreas a little less; I don't understand how revealing every part of his plan to Sam could have hurt. Still, I'm hoping he'll actually redeem himself and explain his entire reasoning behind the whole scheme so Sam can forgive him.
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