After two years on the show, Katy Manning was leaving Doctor Who in 1973. The episode is called The Green Death, and is probably the one of the most tear-jerking departure scenes among a few others in the classic series. It's actually a happy ending for Jo; she meets Professor Cliff Jones, and eventually, after a very rocky start, they get married. The very last scene is actually very sad, the Doctor seems very upset with the departure of Jo. He does not stay to celebrate, and leaves. Jo notices and seems upset as well.
No one heard a peep about Jo after the Green Death episode. Katy Manning moved on and did many things throughout the years, and then the biggest news hit the internet in 2010. Katy Manning was returning as Jo Grant in the Sarah Jane Adventure episode, Death of the Doctor. I literally shrieked when I heard the news. Two of the Third Doctor companions together at the same time, that was amazing. I mean, Sarah has met Tegan and others in the Five Doctors, but not one who worked with the same Doctor as her. The greatest thing about their meeting too, was there was no hostility. Jo comes into the scene just like she always was when she was in the show. Just a little bit clumsy, but still in good spirits and apologetic. That was how Jo was. She may have been a bit clumsy, as we all can be as humans, but she has a great heart, and was friendly to everybody. I liked their introductions to each other so much better than when Rose met Sarah, where they were fighting with one another. Sarah was never mean and hostile to start with, and when she met Jo, it was all warm and friendly. No bitter rivalry whatsoever. That was the Sarah I remember. Jo never changed. I was extremely pleased with the way they wrote Jo in Death of the Doctor, because the writer understood how Jo was, and they wanted to make it just right I suppose. And Katy Manning was able to get right back into her character again after being away for so long. Jo's reaction to the Eleventh Doctor's appearance was quite amusing, and his reply back was just as funny. But the best scene, is when the Doctor, Sarah, and Jo are on the red planet, and Sarah is helping the Doctor fix the device. Jo is standing by herself, and she realizes the Doctor has visited Sarah more than once before, and she overhears he has a married couple on the TARDIS. She then says she only left because she got married. The Doctor than has a talk with her, and tells her right before he regenerated he looked back at every one to see how they were, because he can't really look back at the past. Everything he says proves Jo is more than an idiot. She went from traveling in the TARDIS to saving the environment. If there are fans who have not yet seen any episodes featuring the Third Doctor and Jo Grant, I would strongly recommend Terror of the Autons as the introductory episode is quite good. Another good one is The Curse of Peladon, which is the first of the two Peladon stories in the Third Doctor era. A third choice is The Daemons. It's actually one of the more popular stories, and it's another early story featuring Jo and the Master, but it's very good indeed.