Now in the Tennessee National Guard after serving in the military, Brix Rhodes and his team are called to assist the sheriff's department and highway patrol after a sinkhole appears at the Kentucky-Tennessee border. Since losing his wife, Samra, in a car accident four months ago, he's been left to raise their baby girl alone, but fortunately his dad is always there to help care for her while he's away. Brix promises to return soon from this deployment, but he discovers that's a promise he may not be able to keep.

After another cave-in, Brix is sent down into the sinkhole to attempt a rescue, and soon finds himself being rescued by...himself. There's another Brix Rhodes. A Brix who is similar, and yet different from himself. What's more, his beloved Samra exists here as well. She's not dead, but she belongs to the other Brix. Is he in a parallel universe or some alternate reality? What is happening? Is he dreaming or delusional?

He has to get back to his own world and his baby daughter, but can he survive losing Samra a second time? His questions are answered when the other Brix makes that decision for him, and puts everyone's lives at risk.