A team of scientists, including McKay, Zelenka and Ford, are exposed to a deadly virus. Sheppard goes after one of the scientists trying to escape.

Sheppard is infected with the Wraith retrovirus and slowly turns into an Iratus bug. To provide a treatment, stem cells must be retrieved from one of their eggs.

With everyone having a Sunday off - something recommended by psychologist Dr. Heightmeyer - all of the members of the Atlantis team pursue leisure activities. Rodney McKay and Carson Beckett are scheduled to go fishing; Sheppard decides to teach Ronon Dex about golf; Teyla spends some time in the gym; and Elizabeth Weir has a lunch date with the handsome Mike Branton. Their day off however is interrupted by a powerful explosion near the mess hall killing and injuring several members of the team. McKay thinks he knows the cause of the problem - a device found by two junior members of his team may have turned some of them into walking time bombs by creating explosive tumors in them.