Things go from bad to worse aboard Enterprise when the Romulan marauder attacks a Rigellian ship, and making it appear as if Enterprise is responsible.
Travis and T'Pol come up with a way of tracking the marauder, and a model for a sensor net that will increase their chances of finding it. However, they will need over 100 ships in order to put it into effect. Archer decides that the only way to get that number of ships is to attempt something that has never before been attempted - a joint initiative between Vulcans, Humans, Andorians, and Tellarites.
Meanwhile, aboard the Romulan ship, Malcolm and Trip have enabled life support and attempt to disable warp drive. Although they get the warp drive offline, Trip knows that he must disable any backup systems as well. As he attempts to do so, the Romulans, who have been monitoring their actions, seal Trip inside a hatch, and begin exposing him to deadly radiation. Malcolm is ordered to reconnect the warp drive, or Trip will die. Despite Trip's orders not to, Malcolm complies, but secretly sets his phase pistol to overload within the conduit. When Trip is released, the two of them make their way as far as possible from the bridge.
Back on board Enterprise, Archer's proposed alliance seems to be a success. However, it hits a terrible snag, when Talas, Shran's mate dies from the injuries she sustained at the hands of a Tellarite attack (in the previous episode). Shran is devastated, and insists that the culprit honor Andorian tradition and engage him in combat.
Archer is then faced with a dilemma. The Tellarite ambassador refuses to let his man fight. However, if the Tellarite does not fight, Shran will withdraw the Andorian ships. Believing that this alliance is more important than his own life, Archer substitutes himself for the Tellarite. This leaves Hoshi and Travis scrambling to find a loophole in the rules of the Ushann, which may enable Archer to either win or lose without either of him or Shran being killed. As the duel begins, it appears that Shran has the upper hand. However, Archer recovers, gains the advantage, and offers Shran a final chance to end the fight. When he refuses, Archer takes a final swing with his blade, and...severs Shran's antenna.
Satisfied that Archer (in place of the Tellarite) honored the Andorian custom, Shran deems the matter settled, and the allied fleet searches for the Romulan ship. When they encounter the ship, they have difficulty beaming Trip and Malcolm back, and are forced to engage the marauder in a fire fight. Trip and Malcolm eject themselves into space to be rescued by Enterprise, and the marauder flees at warp speed.
Back on Romulus, as the ship arrives, the Romulans disconnect the pilot who has been telepathically controlling the ship. He's Andorian!