The Seawaters reflect on a beloved teacher who entered their lives in 1961. As the Zodiac Killer's reign of terror unfolds, a shocking suspect emerges.

Allen and the Seawaters lose touch after a trip to a college town, where a student is found slain. Years later, their ailing mentor reveals a dark secret.

As the siblings grapple with the true nature of their mother's bond with Allen, a peculiar gift and a box of clues bring them closer to the truth.