Titus was a cannibalist. He ripped Diode apart for his parts and then went after Servo. They wanted to vivisect the Eighth Doctor after they realised he wasn't a robot. They went after Lucie Miller, and if they didn't get her from Probus, Macrinus, and Domitian, they would enter their tower. They threw Probus into a furnace. They realised that Minerva was under the Doctor's control and managed to get her to obey him by copying the Doctor's voice. (AUDIO: The Cannibalists)
Tardis