After Dr. Daniel Jackson deciphered the code to reactivate the Stargate, Reilly was selected to join Jackson in Colonel Jack O'Neill's team on the first expedition through the device. The team traveled to Abydos and exited the gate inside the Temple of Ra. O'Neill ordered the team to secure the pyramid and scan the perimeter but the group discovered no structures or signs of civilization near the giant pyramid and O'Neill soon ordered them to prepare to return to Earth. Jackson, however, announced that he had been unable to locate the cartouche detailing the address required to return home. Major Charles Kawalsky accused Jackson of lying and pushed him to the ground. Realizing that they were stranded on the desert world, O'Neill ordered his troops to establish a base camp near the pyramid.
When Jackson was dragged off by a Mastadge, he was among the soldiers who stayed at the base camp. After encountering the Abydonians, Lt. Brown radioed Lt. Louis Ferretti and ordered him to keep base camp secured until their return. When a sandstorm hit the camp, the team was forced to retreat to the pyramid for cover. While waiting out the storm, Ra's Cheops class warship landed on the pyramid. Hearing the noises, the team took up defensive positions. When Ra's Horus Guards entered the pyramid, Reilly was hit over the head with the end of a staff weapon and killed. His body was thrown in the prison pit with Ferretti and Lt. Freeman. (Stargate)