When the Doctor was captured by Khrisong, Thonmi didn't think the Doctor was responsible for the deaths of Edward Travers' companion and four monks. While the Doctor was imprisoned, he gave Thonmi the holy Ghanta that had been missing from the monastery for 300 years. Thonmi brought it to Padmasambhava, who then sent him to Khrisong with orders to set the Doctor free.
Thonmi helped Jamie McCrimmon capture a Yeti. He was then ordered to guard Victoria Waterfield, who sneaked away from him when he went to get food for her. He found her being menaced by the captured Yeti, held the Yeti off so she could escape, and let the Yeti out of the monastery.
When the monks left the monastery for their safety, Thonmi stayed behind to help the Doctor. He taught Victoria the "Jewel of the Lotus" prayer to keep her from succumbing to the Intelligence's hypnotism of her. While the Doctor battled the Intelligence, he and Jamie smashed its equipment, defeating the Intelligence. He sounded the gong to bring the monks back, and said goodbye to the Doctor and his companions. (TV: The Abominable Snowmen)
By 1965, Thonmi had became the Abbot of Det-Sen. When Edward Travers visited the monastery in this year, Thonmi was away ministering to children from a nearby village who were suffering from diphtheria. (PROSE: Times Squared)