*A vast Mayan pyramid on P7X-377 contains a strange crystal skull, identical to one found by Daniel's grandfather, Nicholas Ballard, years before. Ballard claimed the skull transported him to see aliens, but was laughed out of academia. When SG-1 investigates, the skull emits and energy that renders Daniel invisible to the others. SG-1 seeks out Ballard, hoping he is the key to finding Daniel, and together they return to the planet. This time, Quetlzelcoatl, a giant ghostly alien, rises from the mist. He invited Ballard to remain behind to study, and gives the others the way to return home. *Source: Back of card