OFFICIAL SYNOPSIS from StarTrek.com
When Hoshi identifies a signal that matches the kemocite Archer planted on a Xindi ship, the captain realizes that this could lead Enterprise closer to the Xindi weapon. He orders T'Pol to set a course. The course, however, requires Enterprise to navigate a dense field of spatial anomalies and the ship sustains heavy damage. Just as it looks like Enterprise may not emerge intact, the ship is hauled out by an Andorian vessel helmed by Commander Shran, who has had dealings with Archer in the past. Shran offers assistance to Enterprise, claiming that the Andorians wish to help the humans in their quest for the Xindi. Though T'Pol is suspicious of the Andorians' motives, Archer accepts. Shran sends his tactical officer, Lieutenant Talas, to assist Reed in repairing Enterprise's weapons. Like T'Pol, Reed is skeptical of the Andorians, but he soon finds himself bonding with Talas — the two have similar backgrounds.
Enterprise and the Andorian vessel head out toward the signal, which leads them to a star system ... and four Xindi vessels. Archer comes to the conclusion that the Xindi are running tests on their weapon at this location. He's correct — as the Xindi Council looks on, Xindi-Humanoid Degra prepares to launch a prototype of the weapon that the council hopes will decimate Earth. Archer decides that he needs to get a better idea of what's going on, so he, T'Pol and Shran take the Andorian ship in closer. The Xindi detect the vessel, and a puzzled Degra halts the test and hails Shran. Shran claims that he's part of the "Andorian Mining Consortium" and is searching for the rare element known as "Archerite." Naturally, the Andorians are really attempting to scan for data on the Xindi weapon.
After returning to Enterprise, T'Pol studies the information the Andorians have gathered. She notes that the device they scanned has the same quantum signature of the probe that attacked Earth — it's the weapon. Archer hatches a bold plan: he wants Enterprise to take the weapon from the Xindi. When the Xindi launch the weapon, its power is undeniable — but it still falls short of expectations. Archer notes that Gralik, the Xindi-Arboreal from the kemocite plant, must have kept his word to sabotage Degra's efforts. Archer wants to retrieve the weapon before the Xindi get to it, but T'Pol notes that it's still emitting high levels of radiation. Shran offers a solution: the Andorian ship is better equipped to withstand the radiation. It can capture the device and then transfer it to Enterprise. Archer, however, insists on commanding the mission. Shran reluctantly agrees.
As Archer and Shran prepare to seize the weapon, Enterprise is detected by the Xindi and engages the Xindi ships in battle. The Andorian ship successfully retrieves the weapon and both ships jump to warp. Archer orders the Andorian crew to contact T'Pol and have her meet them at the rendezvous point. To his surprise, Shran has other ideas — the Andorian commander has been ordered to take the weapon back to Andoria and use it to keep the Vulcans from invading. He releases Archer in an escape pod and sets off for his homeworld. He does, however, feel conflicted about betraying Archer.
Back on Enterprise, Archer tracks down the Andorian ship and hails Shran. He explains that when the Xindi tested the weapon, Enterprise intercepted the activation codes. Archer is prepared to activate the weapon unless Shran hands it over. Shran refuses, but Archer's not bluffing — the weapon begins to arm itself. A stunned Shran manages to jettison the weapon right before it explodes.
Later on, Hoshi informs Archer that Enterprise has received a transmission from the Andorian ship. The message, which was sent in a clandestine manner, contains detailed scans the Andorians took of the Xindi weapon. Archer realizes that, in a small way, Shran ended up helping him after all. With this new information, the crew will be able to learn more about the threat they're up against.