Michael Chabon’s 2000 novel The Amazing Adventures of Kavalier & Clay was a comic-book epic for boys of all ages, and his 2002 fantasy Summerland an ostensible children’s tale with a grown-up pomo polish — all of which somehow makes it seem natural that his latest book, ”a story of detection,” The Final Solution, exploits a young-adult form to meditate on an old man’s sense of mortality. In the early 1940s, long retired to a twilight of beekeeping in the English countryside, an 89-year-old investigator dusts off his distinctly Holmesian cap one last time: A mute 9-year-old German refugee has been robbed of his prized parrot, a bird whose vocal repertoire includes mysterious strings of numbers perhaps connected to Swiss bank accounts or German war codes. One would-be thief is already dead. No mystery, especially one comprising a scant 131 wide-margined pages, should contain so many red herrings, or such a flimsy (re)solution. Chabon’s fans, however, will eagerly clue in on a fine new quality in his nimble voice — something firm, rich, and anything but child’s play.