Time travel is fraught with problems, starting with the very practical one that, while wormholes should make it possible, the physicists tell us, we have no idea how to make or control wormholes. In science fiction, though, we get to assume a solution to the practical obstacles, and look at the really knotty problems.
Such as what happens if you visit the past and change something--big or little--that has important consequences.
In this novella, two time travelers from the 24th century visit the last voyage of the Hindenberg, to study that voyage and her spectacular end. They're horrified and disoriented when the Hindenberg is not destroyed on schedule.
The two time travelers on the Hindenberg and their retrieval team have a huge problem on their hands. Have they created a paradox, or merely an anomaly, despite which the timeline will continue largely unchanged? If they've changed history in some important way, why do they still exist? Can they get home?
Meanwhile, in 1998, Dr. Zach Murphy of the US Office of Paranormal Sciences, is investigating a UFO crash.
This is an entertaining story, and well worth the time it takes to read. It was later expanded into a novel, Chronospace, which I have not read yet but probably will.
I borrowed this book from a friend.