SG-1 is on planet P4S-237, talking to the people there who have been oppressed by the Goa'uld system lord Ba'al, whose emissary Lord Mot comes to the planet regularly to collect a tribute in the form of Naquadah.

The people's elder, Ellori, says a prophecy foretells strangers coming through the Stargate and freeing them from Ba'al's tyranny. It made sense that SG-1 are those strangers. Just then, Jonas Quinn sees and hears Ellori's young advisor, Chazen, say, "Stop talking like a fool. It would be madness to defy Lord Mot." No one else hears it until a few moments later—when Chazen actually says it.

Jonas falls unconscious and is rushed to Stargate Command's infirmary, where Dr. Janet Fraiser finds nothing physically wrong with him—though his MRI does show an area of unusual brain activity. She recalls how Jonas' fellow scientists on his off world homeland of Kelowna suffered from headaches and later schizophrenia from excessive exposure to the Naquadah derivative Naquadria.

Jonas experiences another premonition during a briefing in which SG-1 determines Ba'al hasn't been to P4S-237 for generations because he thought the Naquadah mines had dried up. Mot was hoarding the Naquadah for himself so that he could move against Ba'al. Then Jonas sees and hears Major Carter ask him if he wants Mexican food for lunch—which she doesn't actually do until she comes into his office after the briefing.

Jonas now realizes that he is seeing and hearing the future. The rest doubt him—until he tells SG-1 that a Tok'ra named Sina is arriving through the 'Gate and, moments later, she does so. Sina tells SGC that Lord Ba'al is in trouble with Anubis for allowing the defiant system lord Yu to escape. With Ba'al in Anubis' bad graces, Mot is now in a prime position to replace Ba'al and claim P4S-237 for himself.

Dr. Fraiser discovers a rapidly growing tumour in Jonas' brain. If she doesn't remove it soon, Jonas will die.

This tumour, Carter and Jonas surmise, was not due to Naquadria overexposure but to the long time Jonas had spent in the Goa'uld Nirrti's gene-splicing device ("Metamorphosis"). Her experiments gave him the gift of foresight—but with a fatal price.

Dr. Fraiser wants to operate immediately. But Jonas hopes the tumour will stabilize so he can control it and predict Goa'uld attacks. General Hammond grudgingly gives Jonas 24 hours, under Dr. Fraiser's observation, to come up with some valuable precognizant intel, while Carter, Teal'c, and Colonel O'Neill prepare to return to P4S-237.

Suddenly, Jonas has a vision of Major Carter being wheeled out of the 'Gate room in cardiac arrest. He immediately runs down there to stop the mission. General Hammond decides to err on the side of caution and has Major Carter sit the mission out. Teal'c and Colonel O'Neill go on ahead with SG-15. But later, Major Carter goes into cardiac arrest after an electrical accident at SGC. Had she gone on the mission, she wouldn't have been hurt.

Carter pulls through. Jonas is still intent on trying to control the visions and uses Teal'c's Kelnoreem technique as an aid. He then has a vision of Teal'c and Colonel O'Neill being ambushed at the Stargate on P4S-237 and of the iris on the SGC Stargate opening and an army of Jaffa coming through. He then collapses. Dr. Fraiser immediately wheels him into surgery to remove the tumour. But Jonas manages to tell Carter about the vision, and she warns General Hammond.

While Jonas is in surgery, General Hammond, unable to contact SG-1 or SG-15, has the 'Gate room loaded with armed guards in case the vision comes true. Just then, Colonel O'Neill, Teal'c, and SG-15 come through with some wounded. They had been helped by the people of P4S-237 to overtake Mot and his Jaffa who were, as Jonas saw, intending to ambush them.