While tracking clues from a secret code penciled in the margins of mystery novels at a public library, Derek Knowles-Collier discovers a time capsule that may finally put his haunting past to rest. At Queensview Elementary, sixth-grade students are required to complete a community service unit as part of their school curriculum. Derek was sick when groups were assigned, so he is stuck with what's left: landscape and repair duty at the local cemetery. Derek is not happy about his assignment. When he was very young, his friend Dennis was killed by a car after running into the road to catch a ball. Ever since, Derek has had recurring nightmares. It's a relief when his group's lessons on all aspects of cemetery care are so interesting that Derek doesn't have time to dwell on his experience with death. One day, a book arrives at the library, an anonymous donation. While reading the book, Derek and his group find a secret code written on an inside margin. Through a series of discoveries and deductions, Derek and his friends discover the truth behind Dennis' death, which means that Derek is finally able to put his terrifying memories (and his nightmares) to rest.