The series centered around Dan Vasser, a normal man who, for an unknown reason, begins jumping back in time. He soon learns that each series of jumps follows the life of a person whose destiny he seems meant to change, although it doesn't always turn out for the better. While in the past, Dan reconnects with Livia Beale, his ex-fiance, whom he lost in a plane crash. And Dan may find that Livia has a secret life of her own.

Dan's "shifts" through time occur seemingly at random, the only indication of the shift being a slight flash so brief that even Dan himself fails to notice some of the time. Dan appears to have no control over the shifts, though sharp headaches do precede them. The destination date is usually several decades in the past, but as a sequence goes on he usually moves ahead several years at a time - going from the mid-1970s to the 1980s and so on, as Dan alters a specific destiny. Dan can appear in a different place from where he departed, but he seems to limited to the same general area, for instance disappearing in one airplane and reappearing in another thirty years in the past. Dan can also encounter himself in the past.

The shifts only affect Dan, ignoring any other nearby object. For example, one shift pulls Dan out of a moving car, and the now-empty car proceeds to crash. His personal effects (e.g. clothing, mobile phone, etc.), however, are almost always taken with him (the lone exception so far being a tube of lipstick that fell from his hands when he disappeared).

When travel into the past occurs, Dan vanishes from the present for a period of time that has no relation to that he spends in the past. This creates initial tensions with his family and co-workers, who wonder what has happened to him when he seems to disappear for days. He has used his ability to leave a Time capsule, to resolve the issue with his wife.

Dan's journeys appear to have an innate purpose, which is not always apparent to him, but involves positively changing the destiny of certain people.