Fingers appeals to both the music lover and the fantasy lover, for Sleator has aptly combined the two elements to create a fascinating story about family, the supernatural, and basic human nature. On one level, Fingers is a spooky tale of deception, intrigue and the supernatural; on another level, it is a sensitive story about two step-brothers in a dysfunctional family.

Humphrey is the younger son in the family. He was once a child prodigy who was able to play classical piano pieces at age five. Now he is an awkward teenager whose career is quickly dwindling. Bridget is Humphrey's mother. She is a maneuvering stage mother who has booked darling little Humphrey around the world and has made a lucrative success of it. Luc, Humphrey's father, and Bridget concoct a scheme to reclaim Humphrey's popularity and the money that will support the entire family. However, to do this, they need the talents of the older son, Sam.

Sam is Humphrey's half brother and the narrator of the story. He harbors resentment of Humphrey's popularity, career—and more: Sam, whose father was African American while the rest of the characters are white, is something of an outcast in this dysfunctional family. Nonetheless, Sam is persuaded to write the musical compositions that are the key to Bridget's scheme.

Sam narrates and explains his mother's plan to drug Humphrey, who then thinks he has been a medium for the dead composer Laszlo Magyar. The deception works until an old man begins to show up after each performance and tells Sam things that only the family would know about the music.