McKenna first appears in the film's opening sequence, after the Fugitive Predator's ship escapes the Ultimate Predator's ship and enters the Earth's atmosphere. At this time, Quinn is on a hostage retrieval mission in Mexico. Wearing a ghillie suit, Quinn is in sniper mode when he suddenly sees the ship crashing towards him. He quickly snipes a cartel member and evacuates his spot at the last second. After calling-in his teammates Haynes and Dupree, Quinn finds a Bio-Mask and a mysterious wrist gauntlet, which clamps around his forearm. Meeting up with Dupree, the two suddenly see Haynes' skinned corpse hanging from a tree, before the Fugitive Predator appears and blasts Dupree's chest with its Plasmacaster. The camouflaged Fugitive Predator prepares to advance on McKenna, when the gauntlet suddenly ejects a small throwing disc that injures the Fugitive Predator and slices Haynes' corpse in half. McKenna watches as the blood from Haynes' bisected corpse drips onto the camouflaged Fugitive Predator's face and slowly reveals its true form. When its eyes open, McKenna grabs his knapsack with the Bio-Mask inside, and runs out of the forest as he sees a helicopter pass overhead.
McKenna next appears in a small village in Central America, where the gauntlet has come off his wrist. As government forces arrive, McKenna orders a bartender to mail the equipment to his ex-wife's house. Before he is taken in, McKenna intentionally swallows a spherical gadget that allows the Predators to camouflage.
At the US Department of Defense's base in Chattanooga, Tennessee, McKenna is being evaluated on the mission by a psychiatrist, while government agent Will Traeger and his partner observe through a window. Detailing his alien encounter and accusing his psychiatrist of trying to hide government secrets, McKenna is put aboard "The Loony Bus", where several other soldiers are deemed "insane". He meets his fellow bus mates Nebraska Williams, Coyle, Baxley, Lynch and Nettles.
The bus is redirected to the base of Project Stargazer: a top-secret CIA project lead by Traeger, to study a live Predator specimen. When the captured Fugitive Predator escapes the base, Quinn teams up with the Loonies to seize control of the bus and take kill it. The Loonies meet evolutionary biologist Casey Bracket, and they save her from being killed by a Stargazer operative.
At a bar, the Loonies learn that Bracket was an "on-call" in case there was ever extraterrestrial contact. They also learn determine that the Fugitive Predator is heading for his ex-wife's house, because he mailed its gear there. After the Loonies meet his ex-wife Emily McKenna and learn that the gear is missing, Quinn determines that his son, Rory McKenna, has gone trick-or-treating with the gear, mistaking it for a Halloween costume.
McKenna arrives at Rory's school just in time to save him from a pack of Predator Dogs. The two reunite after McKenna blows one up and Nebraska lobotomizes the other with a drill gun. Their moment is short-lived, however, as the Fugitive Predator suddenly appears and threatens Nettles, Bracket and Rory. Baxley's tourettes accidentally distract the Fugitive Predator, giving McKenna enough time to grab his gun and briefly injure it. McKenna, Bracket and Rory escape inside the school, where the Fugitive Predator finds them and choke holds McKenna. McKenna gives it a device from the gauntlet, before the Fugitive Predator is suddenly grabbed and pulled out the window. A second, larger Ultimate Predator reveals itself and kills the Fugitive Predator while the Loonies escape.
The Loonies take refuge at an abandoned barn.
- "We're Rangers. Isn't posing a threat kind of the fucking point?"
- ―Quinn to his psychiatrist
- ↑ McKenna's actor's (Boyd Holbrook) height is 6ft 1 ½ (186.7 cm), so that is also how tall McKenna would have been.