Killers — John B. Rosenman

What comes first, love or duty? When Diana, a 24th century Supervisor of time travel, learns that Dero is taking unauthorized trips into the past, she has a dilemma. She knows she should arrest him, but she loves him too much. Obsessed, she follows him repeatedly into the distant past to save him from the machine-like killers that police the timelines.

One day he goes too far, threatening the delicate fabric of history itself, and Diana must make a terrible decision.