The only one left / Riley Sager.

The Hope family murders shocked the Maine coast one bloody night in 1929. While most assume 17-year-old Lenora Hope was responsible, the police couldn't prove it. It's now 1983, and home-health aide Kit McDeere arrives at Hope's End to care for Lenora after her previous nurse fled in the middle of the night. In her seventies and confined to a wheelchair, a series of strokes have rendered Lenora mute, and she communicates via an old typewriter. One night, Lenora uses it to make a tantalising offer - I want to tell you everything. It soon becomes clear there's more to the tale than people know. But when details about her predecessor's departure come to light, Kit starts to suspect Lenora isn't telling the complete truth - and that the seemingly harmless woman in her care could be far more dangerous than she first thought.