From Time to Time — Marius Smith

Since the invention of time travel there has always been the danger of misuse of the technology. Two massive time stations orbit the Earth, constantly monitoring history for even the slightest change. William, a vampire from the early twenty-sixth century, has been exiled to Earth's ancient past for a crime he didn't commit. While his human friend Luke tries to clear his name on the time station Epoch, William tries to find a way to return there using the now powerless shuttle he was exiled in. With danger from the future still overshadowing him in the past, he realizes that someone is still trying to prevent his innocence from being discovered. But the crime he was accused of was only the smallest tip of the iceberg, and the threat extends to all human colonies across space and time, beginning with Earth. Against a mysterious enemy operation fro their own future, how can William and Luke prevent the utter destruction of humanity in the twenty-sixth century, not to mention the entire history of humankind?