The Sarah Jane was a spaceship where a renegade member of the Kamishi travelled with a clone of River Song. He was pretending to be a future incarnation of the Doctor - thus the husband of River Song - in a time where the Doctor's TARDIS had gotten lost under unknown circumstances. (AUDIO: Signs)
Behind the scenes Edit
Although not stated in narrative, the name of the vessel sounds like a homage to the Doctor's companion Sarah Jane Smith.