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.

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.