Enterprise encounters a comet; Lieutenant Reed and Ensign Mayweather stop to mine some Eisilium. To their surprise, the Vulcan ship Ti'Mur stops by to also investigate the comet– except they are actually there to observe Enterprise. Meanwhile, Sub-Commander T'Pol has to make a decision: stay aboard Enterprise or return to Vulcan and her impending marriage.
Enterprise is investigating a comet, and Sub-Commander T'Pol learns that the comet contains eisilium, a rare mineral which Vulcan chemists have not previously studied in detail. An away team consisting of Lieutenant Reed and Ensign Mayweather is sent to collect samples. Meanwhile, a Vulcan starship, Ti'Mur, under Captain Vanik suddenly appears with a request to observe Enterprise. Captain Archer is not happy about Vulcans looking over his shoulders but, in the interest of cooperation, he agrees.
The Vulcans then send an encrypted message to T'Pol, which Commander Tucker intercepts, and Archer orders Ensign Sato to decrypt. It turns out that it was not a message about Enterprise, but more personal regarding her arranged marriage. Tucker apologizes to T'Pol for having read her message. She asks him to keep the contents of the letter confidential. Later, she confesses to Doctor Phlox that she has been having trouble sleeping, and he suggests that it might help if she confide in someone. She decides to consult Tucker, who does not share her views on Vulcan culture and customs, and that she must leave. Eventually, she decides to forego her Vulcan traditions and fulfill her duties aboard Enterprise.
Archer decides to "break the ice" between their races and invites Captain Vanik for dinner aboard Enterprise. It is not successful, however, as the Vulcan is unresponsive and dismissive regarding human behavior. Archer concludes the meal by accusing the Vulcan of spying on Enterprise and then asks him to leave. Afterwards, Archer notes that an explosion on the surface of the comet has altered the comet's rotational axis. When the sun rises, Mayweather and Reed begin to have difficulties as the ice begins to crack. They attempt to use the shuttlepod to leave, but it falls into a chasm. Archer eventually swallows his pride and negative feelings to Vulcans by allowing Vanik to help rescue the shuttlepod.