At a Conference of Psychic Sciences, "The Commonality" the Taelon psychic link has been invaded and the secret plans for Earth are known. Katya Petrenko possesses incredible psychic gifts and an interest in Boone. She confronts Zu'or, telling him that the Taelons must change their approach to humans, or they will destroy both races. Katya reveals that a taelon named Ma'el gave some humans the gift to break into "The Commonality". As Katya dies, Dr. Belman performs a brain transfer of all of Katya's knowledge to Boone.

Divers stumble across a strange radiant canister while searching for sunken treasure. Upon opening the canister an alien being known as Ha'gel is released from its prison and assumes the identity of one of the crew and destroys the others. Boone is called to the crime scene and his suspicions are raised when he finds Taelon writing on the empty canister. Upon questioning, the Taelons tell Boone that Ha'gel is the last of an alien criminal caste. Afraid that Earth will learn the truth, the Companion's recruit the help of Beckett to deal with Ha'gel. Ha'gel assumes Sandoval's form, and confronts Beckett.

Dr Belman and her scientist daughter Joyce inject an injured ape with the serum, regenerating its injured organs. Unlike her mother, Joyce is eager to try the serum on a human subject.