Dea was a Telian ambassador who had been sent to seek a peaceful outcome to the war with the Megallan Empire.
Instead, Dea was taken as hostage and placed on a Megallan prison ship. She transmitted an SOS, which was intercepted by the Time Lords on Gallifrey. They, in turn, dispatched K9 to trace the source of the message and to rescue whom he could.
He rescued Dea from her restraints, but she refused to leave the ship. She reckoned that there must be other prisoners onboard and it was her duty to try to free them. The robot dog was at first going to leave her to her illogical decision, but then returned and helped her convert the prison ship into a hospital ship.
Dea became one of the first people to start rebuilding her race — and that of the Megallans — after the devastating nuclear war that had destroyed both home worlds. (PROSE: K9 and the Zeta Rescue)