They Nest

Stressed by marital breakdown and alcohol problems, Cahill freezes under pressure in the emergency room. His superior orders him to take a break, and he retreats to the house he and his ex bought on Orr Island to unwind for a few months. The isolation promises rest, but hints of coming trouble begin to surface.

On Orr Island, at the request of Sheriff Hobbs, Cahill starts examining animal and human corpses with unusual injuries. The work pulls him deeper into a mystery rather than a vacation. The local tension grows as he uncovers more anomalies.

Cahill notices red cockroaches infesting the island and their pincers are unusual. He contacts the university entomology department and learns the African species is obscure. His house is also infested, raising the stakes for the isolated community.

A local man Jack breaks into Cahill's home with the intent to trash it, but the cockroaches kill him in a gruesome fashion. The community's fear turns to anger toward Cahill, suspecting him of the deaths. The incident heightens the sense that something alien is inside the island.

The sheriff permits Cahill to perform an autopsy on Jack. Cahill discovers the cockroach-like insects burrow into people, liquify internal organs, and burst out of the host. The discovery explains the mysterious deaths and heightens fear in town.

The townspeople, now convinced Cahill is involved, mob him and lock him and his girlfriend Nell in jail. The fear spreads as rumors grow that the doctor is responsible for the disappearances. Cahill remains determined to protect the town.

While trying to stop break-ins, Sheriff Hobbs is attacked by Eamon and left in the basement, where the insects finish him off. His body is later found; the situation spirals as the threat escapes local control.

Released from jail, Cahill and Nell start evacuating the locals, prioritizing Nell's mother and the children in her class. They search for a missing pupil and realize the danger extends to schoolchildren. The effort marks a turning point as the community faces immediate peril.

They locate the missing pupil's family and discover cockroaches nesting inside a barn; the creatures are closer than expected. Cahill and Nell realize the threat is active within the town itself. The couple scrambles to warn others and devise an exit plan.

Cahill, Nell, Guy, and Henry flee back toward the town and warn reluctant locals. A swarm of mutant insects is seen flying overhead, confirming Cahill's warnings. The town begins to confront the outbreak at last.

The group gets into a boat to reach the mainland, but they are attacked as they try to leave. The boat is overturned and a fuel pump is set alight to incinerate the bugs. The effort buys time as the military is called to handle the crisis.

The main island threat is contained, but the film closes with the ominous note that one cockroach had reached the mainland. The survivors are left to wonder whether the danger has truly ended. The final shot suggests the contagion might continue elsewhere.