Causality Violation And Circular Causality

A story about a time travel police force to prevent causality violations, i.e., changes to the past, can be the first instalment of a series. Thus, Poul Anderson's "Time Patrol" grew into Time Patrol, an omnibus collection of ten stories of different lengths, and The Shield of Time, a long, tripartite novel.

By contrast, when a circle has been closed, it is complete. Every relevant event in a causal circle has already happened, apparently leaving neither space nor need for any sequels. Thus, three circular causality novels by Poul Anderson, three circular causality narratives by Robert Heinlein and some similar works by other authors have no sequels.

However, we are told that Audrey Niffenegger is writing The Other Husband, a sequel to her ingenious The Time Traveller's Wife. Henry, time travelling involuntarily, has not gone very far or very often into the period after his death. There is scope for his daughter, Alba, to travel further both past-wards and future-wards. 

We cannot have another Time Patrol volume but hopefully we will read more about Alba who might have relationships with men in different periods.