When a Stargate malfunction throws Lieutenant Colonel Cameron Mitchell Dr. Daniel Jackson Lt. Colonel Sam Carter and Teal'c back in time they only have minutes to live. But their rescue by an unlikely duo - Major General Jack O'Neill and Vala Mal Doran - is only the beginning of their problems. Ordered to rescue an Asgard also marooned in 1947 SG-1 find themselves at the mercy of history. While Jack Daniel Sam and Teal'c become embroiled in the Roswell aliens conspiracy Cam and Vala are stranded in another timeline desperately searching for a way home. As the effects of their interference ripple through time the consequences for the future are catastrophic. Trapped in the past SG-1 can only watch as their world is overrun by a terrible invader...