The steamship Atlantica makes way to Boston, but dark shadows trail the ship, staying just out of sight beneath the waves. The ship’s passengers seem unnaturally fixated, staring out to sea with a silent, desperate longing. The investigators’ dreams are plagued by eerie underwater nightmares. And now, a passenger has been murdered.

Suspicion, hidden loyalties, and devious strategy rule the day! Unfathomable puts the players in command of a steamship, but not every player can be trusted. While monstrous Deep Ones stream forth from the crushing ocean depths, any player could secretly be a nefarious cultist or a horrifying hybrid Deep One. The investigators must take care not to turn their backs on anyone—it will take all their cunning to save their ship from a watery grave. Battle swarming Deep Ones, uncover the traitors, and steer the Atlantica safely home in Unfathomable!