The Warlord of Mars (1919)
In the third of Edgar Rice Burroughs's Barsoom series, John Carter, an Earth man transplanted to Mars, is impatiently waiting for a time-locked prison cell to free his wife Dejah Thoris, Princess of Helium, when he discovers that two baddies have a key to the back door to the impregnable cell that they use to kidnap the a fore mentioned Dejah. There follows a protracted chase across Mars from the South Pole to the North by way of the forest city of Kator. Along the way, Carter encounters friends and foes as well as the legendary yellow men of Mars, apts, giant wasps and other wildlife.
This is an old-fashioned all-go novel with John Carter swashbuckling for all he's worth from one end of the planet to the other for all he's worth. It's pure adventure with battles followed by chases followed by battles with leering villains, stalwart fighting men and all manner of literary spectacle. Many times it threatens to bog down into pure pulp, but Burroughs's hand at soaring description and ability to elaborate on his world of barbarism and super science keeps things moving.
The only real flaw is that as the books go on, Carter becomes more and more fatheaded, making the same mistakes over and over. Also, we don't get to see nearly enough of the incomparable Dejah Thoris, who is usually merely glimpsed as she is carried from one confinement to the next.
Unlike the previous two volumes, this one ends with a rousing ending and reunion of all the principal characters, so this one reason why the first three books are generally marked as the Mars Trilogy.