The S.G.C. sends a M.A.L.P. probe through to the planet designated P4X-884, and the image they receive back is that of a beautiful beach. The sky is blue, and a large palm tree blows gently in the wind. The planet appears to be an ideal candidate for an off-world research colony, and SG-1 departs to investigate.

O'Neill, Carter, Jackson, and Teal'c step through the Stargate, and appear instantaneously back in the gate room on Earth. Shocked, the team is told by General Hammond that they have been gone for 15 hours.

Dr. Fraiser gives the team a clean bill of health, though they cannot remember a single moment from their mission. After scrutinizing the video sent back by the M.A.L.P., Carter discovers that the beach image was faked. Hidden on the video is a single frame of an alien room of some sort.

Fraiser arrives with more startling news: more extensive scans have determined that a small implant – smaller than the head of a pin – has been placed in the brains of SG-1, all in precisely the same place in their brains. This provides a reason for some strange behavior from SG-1: their senses have been heightened, especially taste and smell. Teal'c downed an entire pot of steaming hot coffee during a briefing. O'Neill has taken to eating pieces of pie like they were potato chips.

SG-1 is confined to isolation quarantine, and soon "Urgo" reveals himself. A jovial, fun-loving mental projection, Urgo is the manifestation of the alien devices. Only SG-1 can see and hear him, leaving Hammond to wonder if the team is going insane.

Urgo wants to play, wants to eat, wants to learn and experience. That is, in fact, his mission: the implants exist to gather information for the aliens. It is the means by which they explore. Once SG-1 returns to the alien planet, Urgo warns, they will be killed so that the information can be harvested.

Urgo enjoys being with SG-1, and encourages them (verbally and subliminally) to show him new experiences. Meanwhile, they are trying to get rid of him. Carter theorizes that because the implants are electronic in nature, an electromagnetic pulse should disable them.

Urgo tries to distract Carter, but finally pleads for his life, asking Carter not to throw the switch. But she does, and Urgo vanishes. O'Neill rejoices that the annoying man is finally out of his head.

But the alien technology has a reset switch, and Urgo soon reappears. SG-1 decides to pursue the aliens back on the planet, rather than living with Urgo for the rest of their lives. They send the M.A.L.P. probe back through the gate, and use it to broadcast an audio message to the aliens.

A deep, terrifying voice booms back at them. It is that of Togar, who tells them that Urgo is "an error." Urgo was not suppose to reveal himself, and Togar invites SG-1 back to the planet to have the implants removed. Urgo will be destroyed.

The program appears genuinely fearful of his impending fate, and Carter begins to ask him questions. She and Daniel soon conclude that Urgo may be sentient – that he may have become a living being. He is self-aware, he fears his own death, he is conscious, and he can think independently.

The team steps through the Stargate to the alien world, and is instantly transported away in a flash of light. Togar appears, and bears a striking resemblance to Urgo – though not nearly as fun. He promises that they will not be harmed by the removal of the implants, and demonstrates the procedure on another alien life form.

But the team is not satisfied with simply having Urgo removed from their heads. They convince Togar of the possibility that Urgo is alive, and he agrees to transfer Urgo into himself.

With the implants removed and Urgo safe and sound, the team returns to Earth. But their memories have been erased again – they have no memory of Togar or the alien world, though Hammond tells them that they have been gone for more than ten hours.