Scientists have discovered a way to travel back in time. Fearing changes in the past may alter the present, Admiral Jonas Cisco builds the city Sanctuary as a refuge against such a cataclysm. But, an evil man plots to change history for motives of his own. The Gateway, which makes time travel possible is seized. The timestream is broken and the world, as we know it, blinks out of existence. Sanctuary is left alone, isolated. Now Cisco must lead the courageous people of Sanctuary, against impossible odds, to restore the fracture. Time is not on his side.