Forget H.G.Wells'; 'The Time Machine', (great though it was/is), THIS is undoubtedly one of THE best 'Time Travel' stories you'll probably ever read.
I bought a copy of this years ago with a chrome paperback cover,(which looked very cool at the time...in fact, still does!); there was little on the back cover to tell the reader what it was about, only that it contained a story involving 'an appalling mid-air collision' and only slightly alluded to a time in the far distant future; the book was even listed under 'General Fiction'!
The story 'morphs' from, (what seems like) a novel entirely about a mysterious air-crash investigation, into a fully-fledged science fiction story, (not unlike the way the Quentin Tarantino film; 'From Dusk Till Dawn' does).
The chapters alternate between the two main protagonists, and switches back and forth the same way good action/adventure films do before all the 'loose ends' and mysterious sub-plots come together, and this manages to keep you on the edge of your seat until you've read it all...well, it did with me anyway!
Very compelling and well written, with well described characters...just don't let any youngsters read it until you've judged for yourself, as other readers have pointed out, there are some 'adult themes' contained within!
Still one of my favourite Sci-Fi books of all time, I hope it will be one of yours.