Synthetic Men of Mars — Edgar Rice Burroughs

In SYNTHETIC MEN OF MARS, John Carter sets out with his trusted officer Vor Daj to find Ras Thavas, the only man on the planet who may be able to heal the broken body of Carter's beloved wife, Dejah Thoris.

Forced landings on perilous terrain, attacks by hideously malformed soldiers invulnerable to sword-thrusts, the capture of Vor Daj and John Carter, their mysterious transfer to a hidden city on the backs of great birds--these are only a sampling of the hazards the intrepid couple undergo before they finally find Ras Thavas--only to discover that he is trapped by a horror he has himself created--living, spreading, growing, in-destructible tissue which threatens to engulf the hidden city and eventually the planet.