SOLVED. Girl returns home when her father dies and it reopens a mystery about how her sister died years ago. Spoilers ahead. [s]

[Christy]

It may have been set in Ireland, the girl's sister died years ago when the family was staying in a vacation home - I think it turns out the adults had been drugging the kids so they could party without having the kids wake up in the middle of the night. I don't remember much else, there may have been a bracelet that helped solve the mystery, like the girl and her sister had matching bracelets when they were kids or something?

I read it within the last few years, and it seemed pretty new, if I had to guess I would say it was published 2010-2016

[Kris]

Christy, can you tell us more about the girl who returns home - her age, job/skills/interests, family members/friends, is the sister who died older/younger/twin, any romance, etc.?

Is this a mystery for older adults or young adults (teens)? Is it suspenseful?

At the start of the book, what appeared to be the cause of her sister's death?

Can you tell us about the vacation home - location, lake/mountains/etc. ?

[Christy]

So some of this I can't be sure of - I think the sister was younger, but the girl has a twin. Family was so dysfunctional the twin has moved far away (Australia?) and doesn't come back for the funeral. Current age of the girl is in her 20s, early to mid 20s I think

It is suspenseful, I think the big reveal at the end was a plot twist.

I don't remember much about the home. Her father was some kind of real estate developer, and I think it was a house he was flipping. It was a big house maybe on the beach or something, and several couples with various aged children were staying for the weekend.

[Ayshe]

The Darkest Secret?

[Christy]

Yes! Thank you