Vaughn asks Sydney to use her friendship with Sloane's wife, Emily, to gain access to a mysterious Rambaldi book which happens to be under lock and key in a safe at Sloane's home. Meanwhile, Will is kidnapped and told to drop his investigation of SD-6 or risk the lives of his family and friends, including Sydney's.

In order to catch Khasinau and get closer to finding her mother, Sydney and Vaughn set up an undercover transaction for a Rambaldi artifact with Khasinau's representative, Mr. Sark. But Sydney's cover may be compromised when a SD-6 agent is sent in to thwart the sale. Meanwhile, Will is enticed to continue his investigation of SD-6 when he learns the identity of one of his kidnappers. Emily tells Sydney that she knows about SD-6, which forces Sloane to make the most difficult decision of his life.

In order to save Will's life, Sydney and Vaughn must destroy a familiar looking Rambaldi device, while Jack makes a risky deal with Khasinau's representative, Mr. Sark. Meanwhile, the CIA believes that one of their own is a mole for "The Man"; the Alliance comes to a decision regarding the fate of Emily Sloane; Dixon's suspicions about Sydney intensify; and Sydney finds herself face-to-face with "The Man."

Sydney races to find a cure for Vaughn, but in order to find the antidote, Sydney must make a deal with Sark that could endanger Sloane's life. Meanwhile, Will continues his research for Vaughn and discovers some disturbing inconsistencies involving 20-year-old standardized IQ tests.