The story opens with Marcellus, a giant Pacific octopus in the Sowell Bay Aquarium, counting the days of his captivity and the dwindling span of his four-year life. He is sardonic, precise, and very observant, and he has learned to slip out of his tank through a hidden gap to forage for better food on a strict 18-minute clock before air exposure overwhelms him. One night he tangles himself in a phone charger and is saved by Tova Sullivan, the seventy-year-old night cleaner, who frees him and carries the mark of his suckers like a silver-dollar bruise. Their encounter plants the book’s central bond: a quiet, equal exchange of attention between two solitary beings.

Tova’s days are carefully ordered—Knit-Wits lunches with friends Mary Ann, Janice, and Barb; disciplined cleaning; nightly perches on a pier where she imagines her late son, Erik. She has borne two profound losses: her husband, Will, to illness, and Erik, who vanished at eighteen during a ferry-ticket shift in 1989. Authorities presumed suicide after a small household argument and the discovery of a cut anchor rope, but Tova has never believed that story. When her estranged brother, Lars, dies, an attorney presses her to retrieve his effects from Charter Village, a care facility. The errand nudges her to consider a future she has resisted—downsizing to assisted living—and Shop-Way grocer Ethan Mack begins quietly ferrying her through the logistics.

At the aquarium, Marcellus submits to a veterinary check that reveals an odd weight gain—proof of his nightly raids—and he reflects that knowledge eases captivity’s misery. He recognizes Tova’s steadiness, and she grows to speak to him as she works, confiding her dread of nursing homes and the open wound of Erik’s fate. When a fall sprains her ankle, Marcellus slips out, retrieves a missing screw, and deposits it by her shoe, a small act of care that matches the one she once gave him. Tova calls out of work for the first time in her life, and a temporary evening cleaner is hired.

Enter Cameron Cassmore, a hungover musician from Modesto raised by his aunt Jeanne after his mother, Daphne, disappeared. Fired again and newly homeless, he opens a box of Daphne’s belongings and finds a Sowell Bay High School class of 1989 ring wrapped around a photo of Daphne with a handsome teen: a clue that sends him to Washington in a creaky camper brokered by a chatty stranger. In Sowell Bay he meets Ethan, who feeds him and, through a favor, points him to Terry Bailey, the aquarium manager. Cameron bungles his interview but wins a probationary job chopping fish and, temporarily, covering evening cleaning while Tova heals. He and Tova circle each other warily; she trains him in exacting standards and asks him to keep Marcellus’s nocturnal wanderings secret to avoid clamps, lockdown—or worse.

As Cameron hunts for his father, the trail leads to Seattle developer Simon Brinks, whose old yearbook photo with Daphne seems promising. Ethan drives Cameron to a wrong address in the islands—they bond over the mishap—and later Cameron hustles a realtor for the right lead. Around town, rumors stir: at Mary Ann’s farewell luncheon, Adam Wright remembers Erik planning to bring beers to a cabin to impress a girl the night before he disappeared. The name arrives later from Adam’s partner, Sandy: Daphne. Tova verifies the name in the 1989 yearbook, stunned that a missing piece lay so close.

Marcellus, whose health is failing, watches Tova and the new cleaner and notes telling echoes—gait, dimples, flecks in their eyes, even the same toneless hum while mopping. The octopus concludes what the humans cannot see: the young man is Tova’s direct descendant. He decides to intervene. When Cameron leaves his driver’s license on Terry’s desk after a copier jam, Marcellus risks a grueling crawl to steal it and hide it beneath the sea lion statue where only Tova, the meticulous cleaner, ever dusts.

Meanwhile, Ethan pieces together his own confirmation: decades earlier the Shop-Way shamed a six-dollar bad check from Daphne Cassmore, and a glance through an ancestry database links Daphne to Jeanne Baker in Modesto—Cameron’s aunt. He invites Tova to dinner to tell her, but the evening is derailed when Cameron, raw with pride, barges in. Tova, trying to fix the awkwardness, accidentally ruins Ethan’s cherished Grateful Dead shirt while cleaning his counters, then insists on replacing it. The errand forces another choice: on a gridlocked freeway, she authorizes her final deposit to Charter Village, apparently committing to move.

Back at the aquarium, Tova finds the hidden driver’s license and asks Cameron his mother’s name. When he says “Daphne Cassmore,” she realizes Daphne was Erik’s secret girlfriend. Tova shares the full account of Erik’s last night and asks for contact information; Cameron has none—“Not even a birthday card.” Tova briefly allows herself to wonder whether Cameron could be Erik’s child, then pushes the fantasy away.

Cameron secures a meeting with Simon Brinks in a hidden bar Simon dreamed up with Daphne long ago. There, Simon gently but firmly ends the theory: he is not Cameron’s father; his ring bears different initials; he and Daphne were best friends, not lovers; and he last saw her in Eastern Washington, still using. He insists she loved Cameron and could be fierce and private. Cameron, humiliated and spiraling, cancels a paddle date with Avery through her son Marco, miscommunicating at the worst moment, and decides to flee back to California. At the aquarium he vents, claims he was never offered a permanent job, scrawls a resignation, and, in a petty flourish, drops the class ring into the wolf eel tank.

Marcellus, remembering the wolf eel that once maimed him and lengthened his captivity, pushes himself into their enclosure and methodically recovers the ring from the sand. The exertion ravages him. On Tova’s final night, friends bring cake and even Barb softens toward adopting Tova’s cat. After hours, Tova cannot find Marcellus in his tank. At the lobby door she discovers him, pale and drying on the floor. She douses him with tank water, eases him into a mop bucket—and there, on the tiles where he lay, lies the class ring. Turning it over, she reads the engraving inside: EELS—Erik Ernest Lindgren Sullivan. The ring is Erik’s. The clues align: Erik had a girl; a child was born; Cameron is that child.

Tova breaks down alone beside the bucket, then thanks Marcellus for leading her to her grandson. She wheels him through the deserted waterfront to the jetty at an extreme low tide. Marcellus locks an arm with her one last time and slides into the bay. On the pier afterward, Tova meets Avery, who has just realized her son blocked Cameron’s message. Avery recalls talking a distraught woman down from this same spot—someone who repeated “boom.” The word lets Tova finally imagine an accident: a shifting boom knocking Erik into the water after a night of teenage bravado, not a chosen death. She decides she cannot move to Charter Village after all.

On the road south, Cameron’s serpentine belt snaps. He props his phone on the bumper, follows a how-to video, and fixes it—then drives off, leaving the phone behind. Sleep, a shower, and a trashcan for his cigarettes clear his thinking; he turns around and heads north to make amends. At Tova’s nearly empty house, she produces the ring, explains the initials, and tells him the truth: he is Erik’s son. She has pocketed his resignation note, meaning Terry doesn’t know he quit. In Erik’s old room, Cameron pries up a loose floorboard and finds a bundle: Tova’s treasured Dala Horse, flawlessly repaired and hidden by Erik years ago. The find becomes a handoff of heritage and care.

The final chapters resolve quietly. Marcellus, free at last, slips into the deep where he once found a key and chooses his own ending, trusting Tova to look after the injured young octopus who will replace him. Tova sells the house but forgoes Charter Village, moving instead to a waterfront condo. Cameron leaves the aquarium for steady construction work and enrolls in community college prerequisites, insisting on paying his way. On Thanksgiving, Ethan joins them; Avery is on her way; the long-lost duffel finally appears. Tova volunteers at the renovated aquarium, endows a bronze octopus on the waterfront, and retrieves her gray cat. She carries a gentler grief for Erik and for Marcellus, held within a new, hard-won family that grew from attention, decency, and a remarkably bright creature’s stubborn will to set things right.