It has been just 15 minutes since authorities lost contact with inhabitants locked inside a quarantined building overrun with a mysterious virus. Nobody knows what happened inside. A medical officer and a SWAT unit enter the building to monitor the situation and cure those who have been infected…

Doubling-down on the first film’s propulsive sense of escalation, this nerve-shredding sequel doesn’t stop for breath in achieving its admirably uncomplicated goal: to scare the pants off you. The found-footage tech may be upgraded, but the lo-fi fright mechanics retain their effective simplicity.