The Goodies (1970)

S3E4 That Old Black Magic

Witch Hazel's magical abilities are misfiring badly, and she needs help. Turning to the Goodies, they suggest a séance to reach out to lost spirits and get to the root of her troubles. As the session unfolds, Graeme discovers he has an unexpected talent for the supernatural. Unfortunately, his newfound mystical powers backfire in the most bizarre way, leaving him transformed into a gibbon. Now the team must find a way to reverse the spell and get their friend back to normal.