SOLVED. Can't remember the name [s]

[Tiffany]

I read a book last summer about an individual who kidnapped people and trapped them in strange places. I remember one pair was stuck in an abandoned building. The pairs were left in these small spaces with a gun and received notes about if one of them didn't kill the other, they were both going to die. I know this was part of a series and I can't remember the name. The series revolved around the detective and was relatively new.

[Lobstergirl, au gratin]

Tiffany, please provide plot details (no spoilers) and the genre of the book you’re looking for in the Topic header, not something vague like "Help! can't remember this book". Someone is more likely to recognize your book.

[Julia ♡ Sarcasm and Romance Addict ♡]

Eeny Meeny by M.J Arlidge?

"Two people are abducted, imprisoned, and left with a gun. As hunger and thirst set in, only one walks away alive.

It’s a game more twisted than any Detective Helen Grace has ever seen. If she hadn’t spoken with the shattered survivors herself, she almost wouldn’t believe them.

Helen is familiar with the dark sides of human nature, including her own, but this case—with its seemingly random victims—has her baffled. But as more people go missing, nothing will be more terrifying than when it all starts making sense..."

[Tiffany]

That is exactly it! Thank you!