The Enterprise encounters a comet; Malcolm and Travis 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 the Enterprise. Meanwhile, T'Pol has to make a decision: stay aboard Enterprise or return to Vulcan and her impending marriage.
The Enterprise is investigating a comet that has not been plotted on Vulcan star charts, larger than any humans have seen. T'Pol discovers that the comet contains Eisilium, a rare mineral which Vulcan chemists have not previously studied in detail. An away team consisting of Malcolm Reed and Travis Mayweather is sent to collect samples. Meanwhile, a Vulcan star-ship, the Ti'Mur, under Captain Vanik suddenly appears with a request to observe the Enterprise. Captain Archer is not happy about the Vulcans looking over his shoulders but, in the interest of cooperation, agrees. The Vulcans then send an encrypted message to T'Pol, which Trip intercepts, and Archer orders Hoshi to decrypt.
While the crew are waiting, Archer answers questions from a school class in Ireland, and Mayweather and Reed build a snowman on the asteroid. But it turns out that it was not a correspondence concerning the Enterprise but more personal regarding her arranged marriage. Tucker apologizes to T'Pol for having read her message from the Vulcan ship by mistake, telling her that an encoded letter just looked suspicious. T'Pol is upset and asks Trip to keep the contents of the letter to himself. T'Pol confesses to Phlox that she has been having trouble sleeping, and he suggests that it might help if she confide in someone about what's plaguing her mind.
Archer decides to invite Captain Vanik for dinner aboard Enterprise to "break the ice," hoping to establish some level of trust between their species. He is not successful, however, as the Vulcan is disrespectful, and is otherwise dismissive and patronizing regarding the Vulcan's observation and their opinions of human arrogance and inexperience. Archer concludes the meal by accusing the Vulcan of spying on the Enterprise and then asks him to leave. He counteracts by saying that if they had indeed been saying on them they would never have known about it. As he leaves, Vanik talks to T'Pol in Vulcan. She wants advice from Trip who does not share her views on Vulcan culture and tradition, and that she must leave the Enterprise as it is jeopardizing her wedding plans with Koss. Eventually, she does take Trips initial advice and decides to stay on the Enterprise, and forsake the Vulcan tradition.
Archer notes that an explosion triggered on the surface of the comet by the away team has altered the comet's rotational axis. Mayweather and Reed start to have difficulties when the sun rises and the ice begins to crack. They attempt to use the shuttle-pod to leave, but it causes more ice to crack and the shuttle-pod falls into a chasm. Archer eventually overcomes his pride and negative feelings to Vulcans by allowing Vanik to rescue the shuttle-pod, against the Vulcan's expectations.
The episode ends with T'Pol contemplating eating a slice of Pecan Pie after all, which she had previously refused (for being merely mostly just sugar) when offered a taste by Trip, which happens to be his favourite dessert.