In Carry on Again Doctor, Dr Nookey (played by Jim Dale) is a bumbling doctor who is caught in a compromising position with a patient and is sent away to a remote island hospital as punishment. At the hospital, he meets Gladstone Screwer (played by Sid James) who is a member of the staff and is obsessed with creating a slimming potion.
Gladstone gives Dr Nookey the secret slimming potion which he takes, and the results are miraculous. Dr Nookey loses a significant amount of weight and returns to England in triumph. He becomes a celebrity, appearing on TV shows, and giving lectures on weight loss.
However, not everyone is happy with Dr Nookey's success. Some of his colleagues are jealous and try to bring him down by exposing his past mistakes. Others want to exploit his newfound fame and fortune for their own gain.
Amidst all the chaos, Dr Nookey falls in love with a beautiful nurse named Sandra May (played by Joan Sims), but their romance is threatened by the scheming of others.
The movie is full of the classic Carry On humor, with plenty of gags and double entendres. It ultimately ends with a farcical showdown between Dr Nookey and his rivals, with plenty of hilarious mishaps along the way.