Annals of Time

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 human kind 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.