In Without Warning, a radical terrorist group has targeted and seized the Peterson-Daniels Chemical Facility, a vulnerable location that jeopardizes millions of people from the devastating ecological hazard it imposes if destroyed. Pleas are useless and any direct military assault would be too great a risk. As terrified hostages fear for their lives, their only hope lies with a covert operations team, whose goal is to infiltrate the plant and eliminate the merciless enemy.
The Timeline is a distinctive feature that allows the six central characters to experience events across the same period but from their own unique viewpoints. Characters are controlled individually, with the gameplay automatically shifting to the next, often at critical moments. Cinematic cut scenes unfold the plot and by switching between characters, their individual tales are gradually woven together to create an overall picture of the events that happened during the crisis. The player may also retrospectively view events through the eyes of another character and is therefore not only a participant in the events, but a spectator as well. Furthermore, actions performed as one character could affect the progress of others and players must successfully utilize the strengths of each in order to advance.