The Didymus Contingency (Origins, #1)

If you could go back in time... and witness any event... where would you go?

When Dr. Tom Greenbaum faces that question after successfully discovering the secret to time travel, he knows the time, place and event he will witness: the death and failed resurrection of Jesus Christ.

Dr. David Goodman, Tom's colleague and closest friend, follows Tom into the past, attempting to avert a time-space catastrophe. Forces beyond their control toss them into a dangerous end game, where they are tempted by evil characters, betrayed by friends, pursued by an assassin from the future and haunted by a demon that cannot be killed.