Sydney travels to Oxford to steal an ancient clock connected to the Rambaldi mystery. She successfully completes the mission, though Anna Espinosa is hot on her trail.
Jack confronts Sloane about the death of Eloise Kurtz, and admits that he hired the woman, a young SD-6 agent, to impersonate Kate Jones. Sloane, however, did not trust Kurtz and had her silenced.
After her latest trip, Sydney discovers that SD-6 has hired an agent to trail her. Sloane insists that it is merely a routine procedure, but Jack tells Sydney that SD-6 suspects they have a mole. He urges his daughter to seek help from Agent Vaughn on how to fool a functional imaging test -- a sophisticated lie detector.
Sloane gives Sydney her next assignment -- travel to Positano, Italy and have the mysterious clock repaired. The clock was designed by Rambaldi, but built by a master craftsman named Giovanni Donato in 1503. One of Donato's descendants still pursues the family craft, and can repair the ancient artifact.
Meanwhile, Will's editor rejects his story about the mysterious deaths of Danny Hecht and Eloise Kurtz. The story contains questionable facts, and editor Litvack suggests that Will is lying. She demands that he cease his investigation, but Will has other ideas. He is tipped-off to the location of Kurtz's car, and continues playing detective. Inside the car, Will finds a piece of jewelry, which turns out to be a piece of sophisticated surveillance equipment...
In Italy, Donato explains that the symbol on the clock, <0>, is the mark of the Magnific Order of Rambaldi. When Sydney asks about a date engraved on the clock, Donato says that Rambaldi never told him what it meant. Donato realizes his verbal slip, and quickly covers his tracks. The old man returns the repaired clock, and a K-Directorate sniper fires at Sydney. Donato is killed instead, and Sydney narrowly escapes.
Back at home, Sydney reads a book that her father had given to her mother. She uncovers a Russian code embedded on each page...
At SD-6, Marshall discovers that the glass disc from the church in Malaga fits into the clock. When the artifacts are together, a star chart is revealed. Marshall deduces that the chart was made from a specific location on Mount Aconcagua, near the border of Chile and Argentina.
Before Sydney and Dixon can travel to the mountain, Agent Dreyer gives Sydney a functional imaging test. He doesn't reveal the results to her, but he later confides to Sloane that "we've found our mole."
At Mount Aconcagua, Sydney and Dixon discover a tunnel marked with the infamous <0> symbol. Sydney goes in alone, leaving Dixon on the surface. Once underground, she discovers a book with designs from Rambaldi.
Before Sydney can retrieve the book, she hears gunshots through her walkie-talkie. K-Directorate has crashed the party, and Sydney has a fierce fight with Anna. In the heat of combat, Anna grabs the book and crawls back to the surface. As Sydney pursues her arch-rival, she falls from the rickety ladder and plunges into the darkness...