A framing story is told in the first person by Darrell Standing, a university professor serving life imprisonment in San Quentin State Prison for murder. Prison officials try to break his spirit by means of a torture device called "the jacket," a canvas jacket which can be tightly laced so as to compress the whole body, inducing angina. Standing discovers how to withstand the torture by entering a kind of trance state, in which he walks among the stars and experiences portions of past lives.
The jacket itself was actually used at San Quentin at the time and Jack London's descriptions of it were based on interviews with a former convict named Ed Morrell, which is also the name of a character in the novel. For his role in the Sontag and Evans gang which robbed the Southern Pacific Railroad in the 1890s, Morrell spent fourteen years in California prisons (1894-1908), five of them in solitary confinement. London championed his pardon. After his release, Morrell was a frequent guest at London's Beauty Ranch. (Introduction by Wikipedia)