Black Butler: Book of the Atlantic

Ciel Phantomhive boards the luxury liner Campania with Sebastian and Snake to investigate the Aurora Society. The voyage sets the stage for aristocratic intrigue and supernatural danger as passengers mingle with the crew and Grim Reapers.

Three days into the journey, Ciel and Sebastian infiltrate the secret gathering of the Aurora Society aboard Campania. They witness the secret experiments and encounter familiar faces like the Viscount of Druitt and Undertaker. Doctor Stoker demonstrates a device to reanimate a corpse, escalating the danger.

The reanimated woman bites her mother, triggering chaos as the audience flees. Sebastian struggles to subdue her but is overpowered until Ronald arrives and crushes the threat with his Death Scythe. Ronald reveals he was sent to investigate the incidents rather than let them be written off as demon meddling.

Ciel discovers Elizabeth and Snake in the cargo hold searching for him as the hold erupts with coffins and dozens of undead rising. The group fights through the horde while Ronald combats threats elsewhere, buying time for the survivors to regroup. The menace widens as more corpses shamble aboard.

Stoker reveals a second, far larger cargo hold that houses ten times as many awakening corpses. He claims a device in his cabin can halt the outbreak, and Ciel forces him to lead the way to it amid spreading chaos. The ship trembles as the disaster escalates.

Ronald begins reaping souls as the crisis deepens, and Grell Sutcliff surges onto the ship from an iceberg, leaping from the Crow’s Nest to join the fight. The presence of another Grim Reaper intensifies the battle against the living dead.

The Campania floods as emergency doors close, separating Ciel and Elizabeth from Snake, Stoker, and others. Stoker escapes via an elevator while Sebastian remains with Elizabeth’s family to guide them to safety. The survivors brace for a fight on multiple fronts.

Ciel and Sebastian guide Elizabeth and Snake toward safety while pursuing Stoker, only to encounter Viscount Druitt and Undertaker who possess the device. A grand confrontation ensues as Druitt activates the device, but it fails, revealing Undertaker's greater manipulation of events.

Undertaker admits he is the mastermind behind the Bizarre Dolls and the reanimation method, explaining that corpses are animated by false footage appended to their Cinematic Records. The dolls threaten to overwhelm the survivors as the battle tightens.

The first sotoba, a Death Scythe, defeats the reapers, while Sebastian’s Cinematic Record spills out a pivotal flashback to his contract with Ciel and their vow of revenge. The wound is not fatal, but the ship tilts drastically as danger peaks.

Undertaker uses his Death Scythe to slice the ship in half, sending Sebastian and Ciel plunging into the sea. A stray lifeboat is retrieved, and the two halves of the Campania sink, leaving the survivors struggling in the rising dawn.

Bizarre Dolls rise from the water and swarm the lifeboat, drawn to Ciel’s human soul. Sebastian, though mortally wounded, fights them off to protect Ciel as rescue crews close in. He eliminates the last of the dolls before help reaches them.

A rescue boat arrives and transports the survivors to safety. Ciel praises Sebastian for his courage and instructs him to rest once aboard. Elizabeth is also rescued and reunites with Ciel on the lifeboat.

In the post-credits scene, Grim Reaper William T. Spears rescues Grell and Ronald from the wreck and chides them for failing to collect all souls. Ciel reunites with Elizabeth aboard the rescue boat, signaling a fragile, hopeful end to the ordeal.