Rory MacNeil, a rugged old Scotsman, reluctantly leaves his beloved isolated Hebridean island and travels to San Francisco to seek medical treatment. Moving in with his estranged son, Rory sees his life transformed through a newly found bond with his baby grandson.

Vilified by some and venerated by others as the FBI informant largely responsible for the imprisonment of two youths following the 2008 Republican National Convention, Darby was once a charismatic activist mythologized by the American Left for his daredevil aid work in New Orleans’ Ninth Ward in the aftermath of Hurricane Katrina. Informant meticulously constructs a portrait of his life—before and after the death threats—through intimate interviews with Darby and tense reenactments starring the man himself.

As an epidemic of a lethal airborne virus - that kills within days - rapidly grows, the worldwide medical community races to find a cure and control the panic that spreads faster than the virus itself.