On an offworld mission in 2006, his fellow member Babbis fell into a stream. Wallace tried to help him out but lost his footing and broke his own ankle. They returned to Stargate Command and he was sent to the infirmary.
Soon, Wallace was walking on crutches to Major General Henry Landry's office to talk about reassignment. He encountered Sheppard, Dr. Elizabeth Weir, Dr. Carson Beckett, and Dr. Rodney McKay attempting to steal a Puddle Jumper from the hangar. He asked Sheppard if they were going on a mission without him. Sheppard then stunned him with a Zat'nik'tel to prevent him from telling Landry that he had seen them. (SGA: "The Return, Part 1")