He was part of a security detail assigned to guard the Great Eye of Ara, a large ruby considered holy on Orthoo. Garvin stole the ruby, hid it behind a ventilation grid in his quarters, and blamed Sergeant Loi for the theft. Loi submitted to a truth scan, confirming his innocence. When Garvin refused the same procedure, Kirk considered him untrustworthy at best, a thief at worst, and had him transferred off the ship. Kirk felt obligated to pay King Yo 20 million credits as compensation for the missing gem.
In 2266, the USS Enterprise underwent repairs at the Luna repair base. At the Engineer's Club on Earth, Scott overheard Garvin plotting to sabotage the Enterprise. Before Scott could act on the information, Garvin whacked him on the head and dumped him in a disposal center.
Garvin and two accomplices went aboard the repair base and shot security officer Zari. They sneaked aboard the Enterprise and retrieved the ruby, then planted a bomb that he claimed would blow a 40-foot hole in the ship. As they disembarked, Kirk and Leonard McCoy surprised them. The officers were able to capture Garvin and his partners, recover the ruby, and disable the bomb thanks to a telepathic message relayed to Kirk from Montgomery Scott via a vrell. (TOS comic: "Furlough to Fury")