Random thought but could Eustace be a mirror for Mary? According to him he has committed so many sins, according to Homes his guilt is eating away his soul, his past is haunting him and he is a marked man (also Sherlock wants to use him as bait which I thi

Okay I’m in the midst of a bunch of HLV vs TAB work but here are my beginning thoughts in regards to this, because, YES.

What is so interesting is that we are introduced to Eustace through Lady Carmichael’s eyes, very similar to how we are introduced to Mary through John - we only know things about her that John knows, at least for TEH/TSOT. 

One of the first things we are told about Eustace is that he is an acquaintance of Mycroft’s - this is interesting in terms of a Mary mirror. I am not at all convinced Mary is working for Mycroft like Sherlock’s mind palace seems to think, but more likely she is acquainted to Mycroft through more dubious channels of being involved in the Moriarty situation. Possibly?

Anyways here’s where things get even….deeper.

Eustace receives 1) pips and 2) a blank letter. The blank letter reminded me a lot of the A.G.R.A. flash drive - Lady Carmichael sees the letter and “My husband destroyed it, but it was blank. No name or address of any kind.” I would totally like to think that this is the drive, that John saw the contents of the drive, and that it was empty, and after he saw it, it was destroyed. Later, Lady Carmichael goes on to say “He refuses to speak about the matter.“ Sounds eerily similar to Mary talking about her past and the flashdrive. 

And the pips - well there is meta out there at Mary is the final pip but on the other hand I also see the pip as a mirror for the “miss me” video. Eustace knows exactly what it means, knows what it refers to but thought that sender was dead, and is terrified. Similarly, think of Mary’s reaction when she sees the video, and both in HLV and TAB she keeps on wanting to confirm that Moriarty is dead. She is threatened and terrified. If you think about it, she has that reaction in the beginning of TAB as well - “Impossible”

Anyways, so Eustace feels threatened and gets a message from beyond the grave from a bride who we’ve established as a Moriarty mirror already, so you see where I’m going with this. 

At one point he actually sees the bride, saying “my sins have found me out”. Again yet another parallel to Mary, and how CAM was blackmailing her and her past was finally starting to catch up to her.

THEN we get the entire conversation between John, Eustace and Sherlock, which felt to me rather similar to the Mary as client scene also. 

We get John standing between Sherlock and Eustace/Mary. Sherlock deducing a bit about their marriage. “She married you” vs “You chose her”. Mary/Eustace being asked to explain their case in order for Sherlock to help them against an evil. (The only thing I have quite figured out is Eustace saying that he sleepwalks and that it’s a bad dream - how does this parallel to Mary?) 

Mary, like Eustace, has a past. This past originates in America. Eustace/Mary is threatened that their secrets will come to light.

What I think is so great though, and where things get really interesting, taking into consideration previous discussions on Lady Carmichael as a mirror for John. Keep this in mind and then take this list into consideration: 

The take down of Eustace et al “is the work of a single minded person” John/Lady CJohn/Lady C “knew first-hand” of Eustace/Mary “mental cruelty”  
John/Lady C is sent home to help set up a trap where the evil spouse is bait [read: forgiveness scene?]The dark secret, kept from all but John/Lady C closest friends 
A secret kept even from someone who was wronged by the spouse (perhaps saying that Sherlock doesn’t/didn’t know John was against Mary)a message is sent by John/Lady C to distract/send terror to the evil spouse

Lady Carmichael puts the final nail in Eustace’s coffin.

Thus, possibly foreshadowing John putting the final nail in Mary’s coffin?

Still need to think way more on this, but some initial thoughts.