John Carter and the Giant of Mars is a short adventure novel originally published in 1940 in The American Weekly Sunday newspaper supplement and reprinted in 1941 as a Big Little Book aimed at younger readers. Burroughs’s son John Coleman Burroughs is widely believed to have written most of it, with Edgar Rice Burroughs providing the framing and final polish. The novel was not initially included in the official Barsoom canon and was treated as semi-apocryphal until its inclusion in the posthumous 1964 collection John Carter of Mars.
The story has Carter battling a fifty-foot synthetic giant called Joog and rescuing Dejah Thoris from the crazed Pew Mogel, an artificial human descended from the synthetic men of earlier novels. The plot moves quickly. The prose is simpler than the main Barsoom books. The characterization is thin. Worth reading after the main canon if you are working through every published Barsoom text, but not the place to meet John Carter for the first time. Mostly of interest for the way it shows the canon being managed in the late Burroughs years.