A delightfully black comedy, “The Fitzroy” is set in an alternative post-apocalyptic 1950s in which the world is covered in poisonous gas. The last place available to take a traditional seaside holiday is the Fitzroy, a hotel located in a derelict submarine beached just off the coast of England. Bernard — the hotel’s bellboy, cook, maintenance man, and general dogsbody — faces a constant battle to keep the decaying hotel airtight and afloat. But when he falls in love with a murderous guest, Bernard’s challenges multiply, and he becomes entangled in a web of lies, backstabbing, and chaos. As Bernard struggles to hide the femme fatale’s murders from the other guests and suspicious authorities, his world literally begins to sink around him.