In 1872, the American merchant vessel Mary Celeste was discovered adrift off the coast of Spain. Her cargo was intact, but the crew was gone. They were never found. While on a voyage to Africa, an unproven young writer named Arthur Conan Doyle hears of the Mary Celeste and decides to write an outlandish story about what took place. This story causes quite a sensation back in the United States, particularly between sought-after Philadelphia spiritualist medium Violet Petra and a journalist named Phoebe Grant, who is seeking to expose Petra as a fraud. These three elements – a ship found sailing without a crew, a famous writer on the verge of enormous success, and the rise of an unorthodox and heretical religious fervor – converge in unexpected ways.