Not unlike Blake Crouch's previous offering Dark Matter, this one again concerns alternate realities and their interaction. Here they are linked by memories.

Contains some harrowing scenes of nuclear explosions in cities from the point of view of a victim.

The episode on the oil-rig converted to a lab somewhat stretches credulity, but the pseudo-science McGuffin is moderately convincing which helps with the suspension of disbelief. Towards the end started to think "come on, just get on with it and resolve things" but still kept on reading.