Terry (Johnny Vegas) and Gemma (Sian Gibson) of Draper's Tours return with this murder-mystery spoof as they are joined by Mildred (Sheila Reid), Coleen (Sue Johnston) and Hilda (Georgie Glen) on the ferry of a lifetime.After a grand welcome with the crew, terror ensues. A murderer dressed in a dolphin costume wreaks havoc on the ship as passengers get slowly picked off. Coleen is battered with Secretions - a perfume brand available on board the ship, Tracy (Taj Atwal) is shot with a crossbow and the ship's engineer is stabbed with a wrench, after they try to warn passengers.The crew and Terry then search the ship in hopes of finding the murderer while the pressure inside the boat slowly rises as a flood is about to commence. Emily (Doon Mackichan) continues her affair with Alan (Don Gilet) before he is brutally beaten to death with a Choco Mound bar. The remaining passengers gather while the pressure reaches dangerous levels. Pipes begin to burst and the ship's power is cut off. Captain Jack (James Fleet) goes to find the backup generator and upon restarting the power, the passengers discover the body of Emily still stood. Terry begins questioning the motives of Denise (Felicity Montagu) before finding her dolphin costume in the stockroom. Revealing her intentions, she said her plan was to just kill Emily but things had gotten out of hand because she wanted to date Justin (Tony Gardner). She then points a flare gun at the passengers as Jack returns. Denise and Justin try to get to the lifeboats as the flooding continues but they are stopped by Terry and Gemma who distract Denise while Justin shoots her, killing her. Before dying, she reveals she didn't kill Coleen leaving her murder and robbery a mystery. Justin then manages to stop the flooding, saving everyone.As the final passengers escape the ship onto the safe shores of Amsterdam, Terry, Gemma, Mildred and Hilda decide to stop at a riverside café. Hilda then reveals that she mistakenly killed Coleen as she thought she was in great pain when she'd actually confused her with another friend. The two elderly women receive Marge's (Susie Blake in Murder on the Blackpool Express) money that she left to them in her will. The final moments of the film see Terry try to propose Sian before the ring falls into the nearby river due to a cyclist.