This science fiction novel by Colin Wilson is really a novel of ideas, and my teen-age self found it quite compelling, so much so that when I lost my paperback copy I ordered this out of print hardcover first edition. There's an element of fantasy to the book, as it describes the adventures of two scientists trying to find rational explanations for what seem to be nearly mythological forces dating back to the ancient Mayans. The scientists are in pursuit of heightened or cosmic consciousness -- brain operations give them the power to read minds and travel back in time to Shakespeare's era -- and, well, then a bunch of other crazy stuff happens. Wilson said that after he read H.G. Wells at age 11 he wanted to write "the definitive novel about time travel. Time travel is a perpetually alluring idea, but it always sounds so preposterous... The question of how to make it sound plausible is quite a challenge." He pulls it off. 

    This Old Book is a series of posts about books that have survived many purges from my shelves over decades.