A tragic incident shakes human-Vulcan relations to the core when a bomb is set off in a protected area of the United Earth Embassy that claims 43 lives, including that of Admiral Forrest. The bomb detonated just before the High Command may have been announcing its intent to conduct joint missions with Starfleet. In the throes of the blast, Forrest actually saved the life of an extremely grateful Soval. As Enterprise is called to Vulcan after the tragedy, Soval comes aboard the ship with the head of the Vulcan High Command, Administrator V'Las, and his security chief, Stel. With the embassy officially on Earth soil, Captain Jonathan Archer is to handle the official investigation. The initial research from the bomb fragments that Mayweather and Reed extricate finds the DNA fingerprint of a Vulcan, T'Pau. She is a member of the Syrrannites, a zealous Vulcan sect that believes in — among other Vulcan taboos — the practice of mind-melding. Syrrannites follow a corrupted form of the teachings of Surak, the father of Vulcan logic who is considered the most important Vulcan who ever lived. A wanted man named Syrran is the sect's current leader. With a Syrrannite now suspected, V'Las announces that Vulcans will take over the investigation.
Despite the frosty relations Soval has weathered with Archer, he tells the captain that they must team up to find the culprit ? so that one day Vulcans and humans really can work together on a joint mission.
T'Pol's in-name-only husband Koss then arrives on board to give T'Pol an IDIC pendant from her mother, T'Les, which — to T'Pol — is mysterious and portends trouble for her mother. But more surprising, Koss tells T'Pol that her mother is a Syrrannite. T'Pol then finds that the IDIC actually projects a holographic relief map that Syrrannites — currently afraid of persecution — are following. Archer knows that by using this map they can find T'Pol's mother, and T'Pau. However, their journey will take them across a horrific swath of Vulcan desert known as "The Forge,? and once there, all communications will be impossible. As Archer leaves the ship for the inhospitable territory, he warns Trip not to trust the Vulcans aboard as the crew tends to a sick bay full of injured bomb victims.
Then, Trip and Phlox make a fateful discovery when they determine that the DNA on the bomb fragment has been forged. They realize that T'Pol and Archer — whom they cannot even reach right now — may be after the wrong culprit. Determined to find out the true criminal, Trip reviews security tapes from those admitted to the embassy the morning of the tragedy and pinpoints one possible suspect. He realizes that one of the injured in sickbay was the guard who would have seen, admitted, recognized — and known — the culprit. But Phlox warns that the guard is in a coma. Still, Trip is certain that they must have some recourse in finding out more from the man, and suggests to Soval the possibility of a mind-meld. Initially, Soval is aghast at the prospects but soon realizes he has no choice if they hope to find out more about how this tragedy could have happened. Soval performs the mind-meld himself and — to his surprise — realizes that Stel planted the bomb. Confronting Stel and V'Las, Soval hopes to get Stel to admit his wrongdoing and then be brought up on charges with the High Command. But once V'Las and Stel realize that Soval obtained the information that would convict them through a mind-meld, the pair realize they have gotten away with murder. Yet despite the repercussions he may endure, Soval is committed to telling the High Command what he knows ? and how V'Las wants to blame the bomb tragedy on the Syrrannites.
As T'Pol and Archer travel through the inhospitable Forge, they meet up with a stranger who claims his name is Arev. He treats Archer with disdain and is hesitant to believe that he and T'Pol are interested in finding out more about the Syrrannite way of life. Arev — who does not reveal his true identity as Syrran — is reticent to bond further with T'Pol and Archer until he gets a better read on their motives. But, as the three are holed up in Syrran's cave during a sandfire storm, Syrran sees T'Pol's IDIC pendant. He realizes that he knows all about T'Pol, and her missions on Enterprise. He tells her that T'Les is safe with the others in the T'Karath Sanctuary and that — after the sandfire storm dies down — he will take them both there. Further, he speaks reverently of Surak and how one Syrrannite actually holds Surak's "katra? — the essence of his mind. Anyone who performs a mind-meld with this certain Syrrannite also touches the mind of Surak. Then, an explosion rips through the cave, and Syrran is gravely injured. As Archer tries to help the dying Vulcan, Syrran performs a mind meld on an unwitting Archer. In the process, Archer — unbeknownst to him — gathers all the information he needs to take he and T'Pol to the Sanctuary ? and actually now posseses Surak's "katra? as well.
Confused over Archer's seeming omniscience, T'Pol and he arrive at the Sanctuary. Immediately they are attacked, and Archer is threatened with a knife to his neck; the Syrrannites have no idea that he holds the mind — and persona — of their revered leader.