Perpugilliam Brown, of Earth, unwittingly joined the Tardis crew when she leapt overboard of her stepfather's boat. Turlough grudglingly came to her rescue, and left her to sleep in a room aboard the Tardis. She woke and made her appearance in the console at the same time that Kamelion, in the shape of Howard Foster, her stepfather, did, much to the Doctor's surprise and Turlough's dismay. She has short dark hair, a nice smile, and naivete that outdoes nearly every other companion added together. Her sincere desires were to help, but her innocence in the ways of the galaxy left her to accidentally be the cause of much trouble for her and the Doctor.
She helped the Doctor defeat the Master on Sarn, and traveled with him to Androzani Minor, where she fell into a spectrox nest, and became infected with spectrox toxaemia. The Doctor wiped some of it off her leg and became infected as well. They were captured, believed to be gun running for Sharaz Jek, and were to be executed. Jek made android copies of both Peri and the Doctor to be executed in place of the real McCoys, and had the genuine articles brought to him at his hideout. They escaped, only to have Peri captured by the Army. The Doctor and Jek, who was in love with Peri, saved her life. The Doctor gathered her up and carried her to the Tardis, where he administered the antidote to the toxaemia, but there was only enough for her. In an attempt to save his own life, he regenerated. 'Too late, Peri. Going soon. Time to say goodbye.'