The books include prefaces that indicate that K9 is working on behalf of the Time Lords. A total of four books were published: 1. * K9 and the Time Trap 2. * K9 and the Beasts of Vega 3. * K9 and the Zeta Rescue 4. * K9 and the Missing Planet They also suggest that the Doctor's real name might be the Theta Sigma nickname heard in TV: The Invasion of Time and The Happiness Patrol.