Keith Laumer (1925-1993) was a prolific American SF author who specialised in fast-paced adventure stories (of which the Bolo series, concerning intelligent tanks, is best known) and comic satire, notably in the Retief books about an interstellar diplomat. A Trace of Memory, published in 1963, is a stand-alone novel in the former category.
The story is set in the (then) present day with the protagonist a capable but down on his luck American drifter called Legion. He accidentally becomes involved with Foster, a wealthy middle-aged man, who is desperate to flee some unspecified danger. To make matters worse, Foster falls into a coma while they are on the run and, the next morning, wakes up not just restored but rejuvenated. He has the appearance of a twenty year old; but no memory of who he was or what had happened to him.
Legion is drawn along in Foster's search for answers to his identity, a search which ends in the discovery of an ancient control centre from where they trigger the recall of a spacecraft which takes them to its mothership in distant Earth orbit. Foster realises that he originally came from this ship; he is able to recover some general memories of his language and culture with the aid of mental-transfer teaching devices, but is still unable to discover his identity. Foster's people are related to Earth humans, but long ago overcame the disease which causes old age. They are virtually immortal, but every century or so their bodies reset to a younger age, when their memories are wiped. To overcome this, they download their memories ready for uploading afterwards, but Foster cannot find his old memory record.
Foster takes the mothership back to his home planet in search of answers, while Legion takes the shuttle, loaded with saleable high-tech products from the mothership, back to Earth to enjoy a life of wealth and ease. This does not last; he finds himself chased off Earth and decides to take the shuttle in search of Foster. On arrival at Foster's home planet, Legion finds the situation radically different from what he expected and there are various twists and turns before the conclusion.
This book is certainly a page-turner (I finished it in one sitting) with something of the style of an old-fashioned private eye novel; in fact, it reads more as if it belonged to the 1940s rather than the 1960s. I have to admit that while it's a fun read, it isn't brilliant; the characterisation is minimal, there is no mention of women except for the brief appearance of a girlfriend, and there are plot holes which suggest a rather cursory attention to logical consequences. I have a few more of Laumer's books which have been sitting on my shelf for decades, and I hope to work my way round to re-reading them in due course because I enjoyed them as a young lad, but on this basis I'm not too optimistic. Still, at least it's short!