The ship had at least two crew members, as well as an artificial doctor. There was a medical station where the doctor could treat patients, keeping them alive and unconscious even under usually fatal conditions. (TV: The Curse of the Black Spot)
The spaceship became trapped in the same space as the Fancy, with any reflective surface acting as a portal to the other dimension. Though it gave out a distress signal, a disease somehow crossed over from Earth, killing the crew. The artificial doctor began taking injured crew from the Fancy and transporting them to the spaceship for treatment. The crew of the Fancy thought the artificial doctor was a Siren.
The Eleventh Doctor came to investigate the distress signal, but landed on the Fancy instead. Despite his efforts, the Siren continued to take the crew. Once the Siren had taken Rory Williams and Toby Avery, the Doctor, Amy Pond, and Captain Henry Avery decided to go with the Siren in hopes of rescuing Rory and Toby. Once on the spaceship, the Doctor examined a dead alien crew member and realised what had happened. The Doctor and Amy rescued and released Rory, Toby and the crew of the Fancy. Captain Avery, the crew of the Fancy and Toby took the spaceship for themselves, setting off for the Dog Star. (TV: The Curse of the Black Spot)