Ponyville is shaken to its core when a body is discovered in the Everfree Forest. As the townsponies grieve, the mysterious Special Agent Bentgrass from Their Majesties' Royal Investigative Service arrives at the Books and Branches library and drags Twilight into a world she's only read about: lies, corruption, suspicion, and murder.

Faced with an indifferent police force, and Agent Bentgrass's infuriating methods, Twilight must put the pieces together and catch the killer. But as blood continues to spill and questions pile up, one thing is terrifyingly clear: in the dark of the Everfree, much more is at play than mere murder.