S3, E21: Dr. Daniel Jackson becomes intrigued when the video transmission from the MALP (Mobile Analytic Laboratory Probe) reveals a huge Mayan pyramid with a glowing crystal skull in its center. He tells the rest of SG-1 and Gen. Hammond that the skull appears to be identical to one that his grandfather Nicholas Ballard found in Belize in 1971. He goes on to explain that his grandfather claimed that the skull possessed a power to teleport people to a place inhabited by aliens. After the academic community shunned Nicholas because of his seemingly ridiculous claims he never recovered. The team travels to the planet to investigate. Daniel approaches the crystal skull and is drawn to stare into its eyes. Meanwhile the cavern housing the skull begins to emit high levels of radiation. The team starts to evacuate but Daniel is entranced by the skull. Several moments later Daniel's body undergoes a phase shift and becomes invisible. Col. Jack O'Neill Maj. Samantha Carter and Teal'c must flee the lethal radiation leaving behind the invisible Daniel. Teal'c being somewhat protected from the radiation's effects by his symbiote returns to the planet to look for Daniel. When he can't see him he acquires the skull and returns to Stargate Command unaware that he has Daniel in tow. SG-1 solicits the help of Daniel's grandfather whose failure at proving his Crystal Skull theory has landed him in a psychiatric institution. They bring Nicholas Ballard back to Stargate Command in the hope that he can unlock the secrets of the skull and bring Daniel home.