Swan Song

When the body of an up-and-coming rock star is found with his skull bashed in by his favorite guitar, Castle and Beckett begin to probe tensions within his band and his connection to a fanatical religious cult. Meanwhile, a documentary crew that had been following the band around take an interest in their crime-solving partnership and gets permission to record the investigation, prompting everyone—except Beckett—to try to get as much publicity as they can by being the one to solve the case.