The Love Trials by Claire Fraise

A serial killer targets couples in love… But he accidentally takes a pair of enemies instead.

Eden Callahan survived a famous serial killer at thirteen by playing dead while her family was butchered around her. When she’s attacked by another killer at twenty-one and rescued in the nick of time, she discovers a horrifying truth:

Some serial killers come back as ghosts after they die and possess innocent people to continue their murder sprees.
Eden joins a team of paranormal investigators aimed at finding and extracting these ghosts, and quickly begins hunting the most sadistic entity the team has ever encountered. When he was alive, the Game Master got famous for forcing couples into deadly trials designed to break their love, and now that he’s dead, his games have gotten worse.

Eden hunts the Game Master alongside the team, trying to stop him before he kills another victim. But the Game Master has big plans for his next trials, and when Eden gets caught in his crosshairs, she will have to use all her cunning if she has any chance of getting through the investigation alive.