The introduction of Jo is wonderful and sweet. The Doctor's previous episode was Inferno, and Liz Shaw simply left. There was no proper departure for Caroline John as Liz. Jon Pertwee had found Liz Shaw as a companion, too much like the Doctor. He thought the companion should be able to ask questions. Barry Letts found the marvelous Katy Manning. Charming, bubbly and just a wonderful personality all around, she fit the role of Jo Grant. She is introduced in the story, Terror of the Autons, the second Auton story in the Third Doctor's era. The Doctor first assumes Jo is the tea lady when she walks into the room. The research he was working on bursts into smoke, and Jo rushes to help before it catches fire. The Doctor is angry because she apparently ruined what he was working on, and insults her. He then tells her he doesn't want any tea. Jo does not give up easily, no matter how hard of a time the Doctor is giving her. She than goes on to tell him she wasn't the tea lady, but his new assistant. The Doctor's face falls as he mutters his disbelief. Although Jon Pertwee himself wanted a character like Jo, the Third Doctor however wanted someone he could talk to almost on the same level. He was able to do that with Liz Shaw. So when Jo became his new assistant, the Doctor was very adamant at first to not having her. It was Jo's ability to get work done, and standing right in front of him and the Brigadier, when the Doctor decided to keep her on board. But it was due to the Brigadier stepping in and literally putting the Doctor in the spotlight. He insisted the Doctor would have to tell Jo himself. The Doctor could not find a way in his hearts to let her down gently. So Jo Grant stayed. It should also be mentioned in Terror of the Autons, we see the very popular version of the Master, portrayed by the late Roger Delgado. This was his introductory story as well, although it has been mentioned the Doctor has known him since they were both on Gallifrey.