What would Beings from a Type III civilization, able to use the energy of the entire galaxy, do if they decided that humankind was a threat to an arm of that galaxy? Since they had a probation against the destruction of any other species, they would do what they did:  limit humankind to remove the threat by creating a bottleneck event over several hundred earth years, targeting reproduction, cognitive ability, and creating a fear of speed.

But even the most advanced can make mistakes.  And over those few hundred earth years, they left a collection of residuals from their time trips. It caused a minute rip in the fabric of time.

Police Lieutenant Bill Timlin responded to a shooting investigation and drove into that time rip that moved him over 1,000 years into his future. Into a medieval world of limited humans where he had to survive....