The sight of a goose feather at a murder scene modeled after a children’s poem is enough to make FBI special agent Fiona Kelly's blood turn to ice. Almost two decades ago, a feather was left with her sister's body—and with every subsequent victim of the Nursery Rhyme Killer. Now he's back. Only this time, his latest gruesome murder is a message to the only one who ever got away: Fiona.

Finding “Rhyme” is an obsession that's fueled Fiona's career—and destroyed her marriage to fellow FBI agent Asa Kodiak. Now Fiona and Asa have to put their past tensions aside and work together one last time. But Rhyme is watching, and catching this killer may force Fiona to reveal her biggest, darkest secret…the one only he knows.