US Airdate : 27 October 2001
UK Airdate : 7 November 2001

Adam (John Shea) assigns Shalimar (Victoria Pratt) to meet new mutant Donna Morse (Monique Ganderton), also a feral, to ease her transition into the underground for protection from the GSA. When Donna arrives, she informs Shalimar that she's changed her mind and rushes off to meet her date for the evening, Jack Mitchell (Jake Simons). Later that evening, Donna is suddenly overcome by a wave of sickness. Jack becomes terrified and confused as he watches her face transform into a mask of feral rage and pain. With a lightning-quick swipe, Donna sends Jack sprawling before bounding over a high gate nearby.

Meanwhile at Genomex, Eckhart (Tom McCamus) is approached by Karen Bell (Claudia Besso), an auditor. She informs him that she has come across several anomalies, indicating unauthorized research is being conducted in Genomex labs. She assures Eckhart that she will be able to close in on the culprit by monitoring Genomex's computer activity.

When Shalimar tells Adam that Donna has taken off, Adam sends her to Donna's apartment. Finding nobody home, Shalimar slips inside through an open second story window and comes face to face with tall, dark and handsome Richard Saunders (Yannick Bisson), about to hit her with a lamp. As she blocks his attack, her animal reflexes kick in, and a fight ensues. Their struggle soon gives way to a powerful mutual attraction, and they quickly realize they are both ferals. Richard explains he is there to give Donna a treatment. Before he can go into detail, the two are forced to flee at the sound of approaching sirens. Once outside, Shalimar follows Richard around a corner, but he suddenly vanishes.

Back at Sanctuary, Adam and Shalimar discover that Richard works as a research associate at Genomex. In search of answers, Shalimar enters Genomex undercover, finding Richard who reveals that he has developed a serum to reverse genetic mutations. He explains that the treatment realigns the genetic code, causing all traces of mutancy to disappear, and that he has been administering the serum to Donna. A security warning suddenly flashes on his computer, indicating that someone has broken into his files. He and Shalimar take off, managing to overpower the two GSA agents arriving on the scene with Karen, who is furious to discover that all of Richard's files have been deleted.

Richard and Shalimar head back to Donna's apartment where they finally acknowledge their strong feelings for each other. Richard reveals he has been injecting himself with the serum and suggests that Shalimar may also want treatment so they can share a normal life. Hesitant, Shalimar brings a vial of the blue serum to Sanctuary for Adam to evaluate. Before he can warn her that the serum creates uncontrolled DNA breakdown, she decides she wants to be with Richard and takes an injection.

At Genomex, Karen informs Eckhart that during a Jane Doe autopsy, unidentifiable DNA was found that was believed to be purposely altered. Eckhart orders the body to be transferred to the lab for examination. At the same time, Adam, Jesse (Forbes March) and Brennan (Victor Webster) hear about the unidentified victim. Adam realizes it is Donna, concluding that the serum must have killed her.

Back at Donna's apartment, Richard suddenly awakens trembling, his mutant powers taking control of him. When Shalimar takes him to Sanctuary for help, Adam reveals that his condition is fatal, but believes he can harvest Richard's bone marrow, creating a protein antigen to neutralize the small dose of serum Shalimar took. At Richard's insistence, a heartbroken Shalimar agrees to the procedure, knowing it's her only hope. Meanwhile, hope has run out for Karen, who is taken away by two of Eckhart's agents for failing to capture any new mutants or the source of the unauthorized research.