In the mid-22nd century, the Earth ship Enterprise is launched under the command of Captain Jonathan Archer. When the crew rescues an alien from a crashed spaceship, Earth gets its first look at the alien's race - the Klingons. Archer and his crew must walk a fine line as they attempt to communicate with the Klingon pilot, whose language is completely unknown, and whose homeworld wants him back. Is this the beginning of friendship...or interstellar war?

Captain Jonathan Archer, T'Pol and Trip meet Sarin and she explains that Klaang is a courier, bringing an important message from her to the leaders of the Klingons in Kronos about rebels Suliban that intend to promote the Temporal Cold War among the Klingons. Archer feels the need of rescuing Klaang and travels to the Suliban mother-ship with Trip to bring the Klingon back to Enterprise. T'Pol seems to understand that loyalty is an emotion that cannot be avoided by humans.

Enterprise has a group of aliens watching a stellar phenomenon on board. When the ship is miraculously saved from blowing up, crewman Daniels has an important message for Archer.

Enterprise discovers a mining colony of the Paraagans. The crew gets an invitation for a meeting on the surface and a shuttle pod tries to break through the atmosphere. All of a sudden just under the shuttle a giant explosion begins and scorches the earth beneath. All 3600 colonists are reported dead. After examination, Enterprise finds out plasma leaking from the pod's vents ignited tetrazine in the atmosphere. Lieutenant Reed, however, ensures he closed the plasma vents before the shuttle went of. After conversations with admiral Forrest of Starfleet Command, Captain Archer learns that Enterprise's mission is canceled and they must return home, not to return to space for another ten or twenty years. When the ship has altered course, crewman Daniels, a time traveler, pays a visit to captain Archer.

Captain Archer and temporal agent Daniels have been stranded in the 31st century. In a library they investigate the damage to the time line and try to find way a to get Archer back in his own century. Meanwhile Silik the Suliban leader is trying his utmost to find the whereabouts of Archer and he is willing to go far for the answer. But the crew of Enterprise has plans of their own. Trip finds a way to use the com system and is able to speak with Reed. Together they try to contact other crew members and make plans to purge Enterprise of the Sulibans.

An alien probe launches a devastating attack on Earth. Archer, still being hunted by the Klingons, brings the Enterprise back home to investigate.