Everyone on This Train Is a Suspect

That's the good stuff right there. I think I remember having a similar experience with the first book in
this series, that I was enjoying myself riding along with the attempted mystery solving, then got a bit
iffy in the reveal, as there were certain things I'd already guessed, and then other things I hadn't had a clue about that were just barely believable, and
then it was how the book actually ended that settled it for me, in focusing back on the characters
and their relationships, experiences. Stevenson provides an empathetic, yet all-too-human perspective in Ernest and it makes all the difference in having him as the narrator. Sometimes the interpersonal drama leans thriller-esque, but I know I'll always have one character I actually like. Though that other theme running through the book leading to the epilogue is what truly made it for me. As always I'll caveat that I'm a fairly gullible, easy going mystery reader so those in it primarily for the puzzles may not be as entertained as I was.
I recognize that it's a personal preference that violence against women, SA, not be a plot point, even though elements of the scenario are tragically similar to real life publicized accounts. In this sense the formula and tropes that Stevenson plays with may work in my favour. Having used it so prominently once, it's unlikely to return in the next book. I look forward to continuing in the series, hopefully the author plans to do so!