After the death of her husband, Tova Sullivan finds solace working the night shift at the Sowell Bay Aquarium. Keeping busy helps her cope with a deeper, older grief: the mysterious disappearance of her eighteen-year-old son more than thirty years ago. Her quiet, orderly life takes a turn when she befriends Marcellus, the aquarium's giant Pacific octopus. Tova soon discovers that Marcellus is a remarkably intelligent creature with a knack for escaping his tank and a keen observational eye for the humans around him.
Elsewhere, a young man named Cameron Cassmore travels to Sowell Bay, adrift and in pursuit of the father he never met. His search leads him to a temporary job at the very same aquarium, setting his path on a collision course with Tova's. What unfolds is a story of three seemingly separate lives, woven together by an unlikely friendship with an octopus who holds the key to unlocking a long-unsolved mystery. This novel explores how examining the past can reveal a future that once seemed impossible, revealing the profound connections that can be found in the most unexpected of places.