In July 1977, while looking for an entrance to Fetch Priory, Leela was separated from the Fourth Doctor and came across the Tyler cottage. Ted Moss was alone within and fired a gun at her. She avoided harm and had turned the weapon on him when Jack entered and, pressing a cane against her back, convinced her he was armed and so she handed the firearm over. He asked them to explain their presence. Jack found Leela's story unbelievable and, when Moss said he had come for what Martha owed him, Jack said he would get it.
Moss left and, after a time, Martha returned home, visibly in shock. Jack and Leela helped comfort her. She spoke of something "hungry for [her] soul" and Leela left to get the Doctor's help. Martha was revived to her senses by talk of commonplace things - tea and fruitcake - and she told the Doctor, Leela and her grandson about what she had seen in the woods. She told the Doctor it didn't have a human form, but when he and Leela had gone, she told Jack it was a woman. Before he went, the Doctor asked Jack to keep an eye on the priory and, while carrying out this request, he saw a van pull up outside the building and Ted Moss and three others get out.
At home, Martha asked him to take one of her charms. While he told her he didn't believe "in all that", he agreed to take it to please her. When asked, he also gave her cartridges from his gun to fill with salt, which Martha said was the "best protection". She told him he was best heading to the priory, adding "we don't want 'em meddling in things they don't understand".
Both Martha and Jack went to Fetch Priory and met the Doctor and Leela there. A Fendahleen paralysed the legs of all three humans and, taking Jack's rock salt-primed gun, the Doctor killed it to free them. After Adam Colby was freed from the cellars by the Doctor and Leela, he join the Tylers and Jack warned him against criticising his grandmother, whom Colby blamed given that her visions were the impetus for Maximillian Stael's plans.
Jack was present as the Doctor explained the nature of the Fendahl, it being a gestalt creature - a description Jack queried and which Colby explained to him. Armed with more rock salt, the Doctor had Jack and Leela keep watch in the corridor beyond Fendelman's lab. The Fendahl core - in the image of Thea Ransome - and a Fendahleen appeared before them. Leela told Jack to fire but, having looked into the eyes of the core, he was unable to do so. Leela knocked him down, took the gun and killed the Fendahleen. After Martha finished collecting salt for the Doctor's usage, he told the Tylers to return to their cottage. They sheltered under a table, where Colby joined them after a time, as Fetch Priory was engulfed by the flames of the Doctor's controlled implosion. Having fled the priory themselves, Leela asked the Doctor if it was okay to leave the others, and he told her "Yes. Probably at Mrs Tyler's now, eating plum cake off her best china." (TV: Image of the Fendahl)