Mystery was a female cat that resided on the USS Enterprise-D in the 2360s.
Biography[]
Mystery basically considered the Enterprise to be her domain, and wandered the ship largely at will. No one was ever able to figure out how she got around force fields and doors, hence the name Mystery. Several concerted efforts were made by the crew to keep her in areas appropriate for pets, however these attempts were unsuccessful. In 2364, chief medical officer Dr. Beverly Crusher largely gave up on trying to keep her out of sickbay once she realized that Mystery never entered quarantine areas, and chalked her behavior up to cats having senses that people would never understand. While she was friendly towards most individuals, she never purred for Lieutenant Commander Data, not being quite sure what to make of him.
In an alternate timeline where Data was transformed in to a human being by the "Gods" of Elysia, Mystery managed to enter Data's quarters as he prepared to go to sleep for the first time, and kept him company while he slept.
In the prime timeline, Data was never transformed into a human, and realized that the Konor were not telepaths like Vulcans or Betazoids but simply a group of Samdians that developed the ability to broadcast their thoughts over radio waves that Data could also receive. Building a transceiver he was able to communicate with the Konor and convince them to stop attacking their fellow Samdians. As Lieutenant Geordi La Forge and Doctor Katherine Pulaski worked to repair the damage to Data caused by the transceiver, Mystery jumped up on the bed for a closer look and moved to touch a diode flashing inside Data. La Forge and Pulaski took Mystery and asked Data to hold on to her while they finished the repairs and closed up his body. Data did so, holding Mystery next to his head. Data then reported that Mystery had started purring. (TNG novel: Metamorphosis)