Disguised as locals, Archer and his expedition explore a civilization bedeviled by a virulent ailment possibly linked to a covert -- and anomalous -- nuclear reactor. Determined to find the truth, the captain teams up with a local apothecary, leading to a close encounter between the two.

The Enterprise comes in contact with an alien vessel transporting stargazers to observe a spectacular stellar event. They are Borothan pilgrims who have come to see the Great Plume of Agosoria, a phenomenon their religion associates with the beginning of the universe. Archer invites them aboard the ship to witness it, not realizing that the Suliban agent Silik is among them. Archer quickly realizes that Silik is engaged in a nefarious time-traveling mission and must stop him before he can tamper with the course of history.