For peek-between-the-fingers moments, it's hard to top a sex scene lubricated by the revolting promise of a flesh-eating virus. Cabin Fever: Patient Zero -- the third installment and prequel of the series that began with Eli Roth's 2002 woodland gorefest -- delivers its share of anticipated gross-outs, which director Kaare Andrews presents with a sly, often lipless, grin. The fun begins as four old friends charter a boat to drop them off for a bachelor-party trip to a remote Caribbean island, supposedly deserted. Unfortunately, the north side of the island is home to a secret disease-research facility, currently under quarantine, thanks to Porter (Sean Astin), an unaffected carrier of a deadly virus, who's dead set on escaping. (Symptoms include jellied flesh sloughing off the bone; manic desperation; vomiting forceful gouts of blood.) Poisoned by snorkeling in contaminated water, the revelers start heading toward the lab for help. It takes the two groups a little too long to meet -- the film sags as characters wander through a maze of underground corridors -- but patience is rewarded by a terrific gag with a handgun and a catfight that plays like a long-lost Tom Savini-directed episode of Dynasty. Vincent Guastini's makeup effects are the star here, a refreshing change from the inky CGI morphing of too much modern horror.