US Airdate : 12 January-2004
UK Airdate : 16th June 2004

Jesse (Forbes March) and Brennan (Victor Webster) are playing Tunnel Quest II, a new virtual game Jesse downloaded to Sanctuary's system. The two vigorously use their keyboard to maneuver virtual images of Shalimar (Victoria Pratt) and Lexa (Karen Cliche) battling two combat soldiers. Engrossed in the game, Jesse and Brennan don't notice the real Shalimar and Lexa lurking over their shoulders. When Brennan proposes a virtual shower scene with sexual overtones, Shalimar and Lexa are less than amused and demand they erase the game. To keep the peace, a disappointed Jesse caves in and deletes the file.

Later that afternoon, Shalimar hears a noise outside her bedroom and warns the team that she doesn't think they're alone. All of a sudden, the climate-control breaks and the temperature in Sanctuary soars. As Jesse begins working on overriding the system he sees Sergeant Nalle, one of the characters from the computer game, on the monitor. Confused, Jesse deletes the game once again. Meanwhile, Shalimar and Lexa are investigating the sound Shalimar heard when an electric panel behind them suddenly bursts into flames. Distracted by the flames, the girls don't realize that the security cameras are watching their every move. In the master control room, Jesse realizes an unknown source is hacking into their system. Suddenly, the security system identifies Shalimar and Lexa as hostiles and the doors begin to close in around them. Jesse tries to override the system, but is unable to gain control and Sanctuary goes into lockdown. Jesse comlinks Shalimar and Lexa and insists they use the Helix to get out of the building before it's too late. Taking Jesse's advice, Lexa manages to thrust the aircraft through the closing hanger doors just in the nick of time. Seconds later, Jesse and Brennan rush towards the Helix, but the doors close around them, trapping them in the hanger.

Meanwhile, William Dennett (David Orth), a disgruntled quadriplegic with cybernetic mutant powers, lies in bed at a care facility. A series of wires connect his head to a computer, allowing him to control Sanctuary's impenetrable security system. Pretending to be Brennan, William comlinks Shalimar and Lexa and tells them to head to a nearby warehouse where Adam installed an emergency back up system. The vindictive mutant then creates fake rap sheets for the girls, listing them as ?FBI's Most Wanted? and places a call to 911 reporting their whereabouts. At that moment, Helen (Lynne Cormack), William's nurse, barges into his room. Annoyed by her presence, William provokes her by speaking through his computer causing her to drop his medication. Fed up, Helen moves to unplug the computer, but is suddenly paged over the PA system and leaves.

Back at Sanctuary, Jesse has just finished repairing the climate control when the hologram of Sergeant Nalle reappears, aiming his gun at Brennan and Jesse. When Sergeant Nalle fires, the two leap out of the way and as Brennan hits the wall behind him, the high voltage of the hanger's defense system electrifies him and pins him down. Locating the circuit panel, Jesse masses out and stops the deadly current with a massive punch and Sergeant Nalle disappears. Still unsure of who is trying to kill them and why, Jesse and Brennan are now painfully aware the attacker is familiar with their mutant powers. Meanwhile, Helen re-enters William's room and disconnects him from his computer by slowly pulling the electrodes off his head one-by-one. When William's monitor indicates that he is flat lining, a panicked Helen tries to revive him, but she is suspiciously electrocuted in the process. William, alive and in control, is certain there will be no more interferences in his plans with Helen now out of the picture.

Arriving at the warehouse, Shalimar and Lexa find the police waiting for them and use their combined mutant powers to escape. Knowing Brennan would never mislead them, Shalimar realizes that they've been set up. She then comlinks Brennan, and becomes even more suspicious when she hears the person on the other end utter a phrase that William Dennett had said right before falling off a building to avoid capture by Mutant X years earlier. At that moment, William reverts back to his true voice, confirming to Shalimar that he is behind what is happening at Sanctuary.

Back at Sanctuary, Brennan crawls inside the air duct looking for an escape route, but there's no way out. Just then, a hologram of a healthy looking William appears in front of Jesse and shoots a barrage of lasers at him, which Jesse avoids by phasing out. When Jesse reappears, William shoots him in the arm. Brennan then dives out of the air duct and fires off a tesla coil at the laser control unit and the hologram of William disappears. Moments later, a deadly white gas begins seeping into the room. William's hologram appears again to inform them that the gas will slowly paralyze them and they will finally understand what he's been living with ever since his fall. As the gas starts to take effect on Brennan and Jesse, Shalimar and Lexa, who have tracked William's location, burst into his room and manually override the program, saving their teammates. With Sanctuary back to normal, the Mutant X team relaxes with the knowledge that William can no longer get to them. Little do they know, William is busy searching for another medium to manipulate in his quest for revenge on Mutant X.