Darwin had it half right
Chicago – 17 years ago
A young girl, Kate Allen Benson, is called to supper by her mother as she stares out the window. Her mother insists she say there's nothing outside and Katie goes to supper… as a pair of claws grab at the sill.
In Chicago, Kate Benson and her partner are running stakeout and Benson thinks there's a pattern to the recent series of abductions of young girls based on the time of day and the direction of the streets. Her partner is skeptical and warns her weird theories will get her in trouble with their superiors. As he heads back to the station, a mysterious man watches them and a young girl goes into the nearby apartment block. Kate sees her and goes in after the girl and tries to get her out. The door closes behind them on its own and a hooded figure approaches them. Kate shoots it repeatedly with no affect. Kate recognizes the creature… and then the man from outside comes in with some kind of energy weapon and blasts it to pieces. Another one grabs the girl and yanks it through a window before they can act. The man tells Kate she'd better come up with an explanation as he leaves, and the police come in to demand answers from Kate.
Kate gives her official report but her past reputation for reporting bizarre stories ends up getting her suspended. The man outside confronts her and Kate tries to arrest him, inadvertently blowing up a police van with one of his special weapons. He finally shows her his wallet, which identifies him as Nicholas O'Malley with the Chicago Police, Special Unit 2. He wants to take her to the station house and she finally agrees.
The "station house" is underneath a dry cleaners in an abandoned subway line. Nick turns Kate over to his boss, Captain Richard Page, who wants her both to make it look good that they have more women and because she's inclined to accept the supernatural. Page explains that the creatures known as monsters are evolutionary creatures halfway between man and animal called Links. Page draws a gun on her then calls in a gnome creature that comes charging in and he puts several bullets in it. He then introduces Carl as a gnome, and their bulletproof snitch and mascot. As she's passed the initiation, Page brings her on in a temporary basis.
Page shows her they're special ammo for Links and partners her with Nick, and explains he lost his partner a few years back. Their tech advisor, Sean Redmon, explains that gargoyles reproduce by lying thousands of eggs and as the hatching time arrives, two guardian gargoyles start collecting live victims to use as food for the younglings. The eggs are due to hatch in 24 hours and the SU2 teams hit the street.
Nick and Kate are driving around and she comes up with a theory that other Links know how to avoid the gargoyles. Nick drops off a package with a kid then goes to a convenience store where they find Carl the Gnome robbing the place. Carl and Nick don't get along but eventually Carl reveals that the Links are avoiding Merritt Park. Kate goes in as a decoy while Nick reveals he stole the film from her previous case. A gargoyle closes in on Kate and Nick manages to snag it with a net gun.
The gargoyle Little Brother proves resistant to interrogation so they keep hitting him with weapons until they find a shrinking gun that works. It gives up the location of the nest and Nick and Kate head there with the now 6" gargoyle in their pocket. Kate hints around what happens with Nick's partner and he talks about how he ordered them to split up and his partner got killed, and now he sends money to his partner's kids, like the one he met earlier.
SU2 enters the building which is an old police station, and they realize it's a trap. Nick shoots Little Brother dead as the gargoyle closes in. It grabs Nick and escapes.
Page and Redmon search the building and interrogate Kate, but they don't turn up anything except Nick's weaponry and some rock dust. With two hours left, the Big Brother gargoyle takes Nick to the nest while Kate and Sean go to Carl who can identify the rock samples and place their location near a coal plant.
Big Brother boasts of gargoyle supremacy as the eggs start to hatck. Nick manages to cut himself free but the gargoyle is too powerful for him. The SU2 squads arrive at the coal plant that meets the criteria and Kate has them blast the caps open.
Big Brother throws Nick around until Kate comes down on her own and throws Nick the gun. He shoots the gargoyle repeatedly until he shatters it into pieces. They rescue the prisoners and Nick cheerfully torches the eggs.
Kate goes back before the review board who discover that she's received a promotion and a transfer to Special Unit 2. Nick and Carl meet her outside and welcome her on board and let her know the prisoners were all convinced they were hallucinating. Nick thanks Kate for saving his life and she asks him to make up with Carl. They shake and head back to the station, Carl and Nick fighting all the way.