In a shocking turn of events, Peso 'dies' during a mission, leading to a blame game among the crew. Barnacles, the captain, is unfairly accused by Dashi and Kwazii, leaving him feeling burdened with guilt for what happened to Peso. However, Shellington and Tweak maintain their trust in Barnacles, believing it was just an accident.
But when Shellington is mysteriously poisoned a week later, tensions rise within the Octonauts. Tweak loses her trust in Barnacles, and Inkling, the team's founder, demotes the captain to a Detective—a role he struggles to embrace, being better at solving game mysteries than real ones.
As time passes, Peso is miraculously found alive and uncovers proof of Barnacles' innocence. It becomes clear that the real target of the poison was Barnacles all along. With Barnacles himself falling victim to poisoning, can the crew save their captain and mend the broken trust, or will this new enemy tear them apart and snatch their leader away?
