Fred Hoyle 
October the First Is Too Late [EPUB ebook] 

The Yorkshire Moors below Mickle Fell in August would seem a safe enough place to be, yet it was there that Richard’s old schoolfriend, John Sinclair, disappeared for 13 hours. Two days later, while bathing in a mountain stream, Richard noticed that a strawberry birthmark was missing from Sinclair’s back. Climbing, music, ancient Greece and the year 5000 AD: all these play a part in Fred Hoyle’s far-reaching and witty science fiction book, which teems with arresting ideas. Its central themes are time and the meaning of consciousness; around them the author of The Black Cloud and Ossian’s Ride has spun a glittering web of adventure and logical surmise. In this world of dual personalities and shifting time scales it is entirely plausible that October the first should have been too late.