An excellent example of "theological" science fiction, set 700 years in the future. Several young students of an atheistic school join an expedition to find a time portal through which one might probe the mystery of Christ's resurrection. The journey is fraught with sex, economics (?!!), dancing, drug-taking, and encounters with hostile alien cultures! 192 pages.
Used availability for Brian Earnshaw's Planet in the Eye of Time
October 1968 : UK Hardback