The Jester at Scar by E C Tubb (1970)
Scar is a viscous world. Circling close to a red sun, its winters are a long night of cold monsoons and the summer an endless day marked by impossible growths of fungus that are at once incredibly valuable and unbelievably deadly. It is to this world that Dumarest has come in order to race a stake to finance his hunt for Earth. Meanwhile, a strange couple have come to Scar on a seeming whim; the ruler of the planet Jest and his new wife who is a noble from a violent, puritanical world. As Dumarest fights against the deadly ecology of the world in quest of his fortune, he must guard his back against a shadowy someone who has made more than one attempt on his life and has a curious interest in rings that look similar to the one Dumarest wheres.
And, as always, the Cyclan are never far away.
The fifth in the Dumarest Saga, The Jester at Scar is something of a breather for us. Dumarest is in possession of the secret that the Cyclan will stop at nothing to recover, but he is still unaware that it's been passed on to him. The action here is hard and gritty with vivid descriptions of a world that goes from barren, muddy wasteland to riotous jungle in a matter of days. Tubb also shows that even though he's writing a formulaic series, he can still take the time to provide subplots of reform and redemption as well as an intriguing portrait of a character done in broad strokes who at first seems like a madman who makes life and death decisions based on the spin of a coin, but turns out to have very practical reasons for doing so.
Not as high adventure as other books in the series, this one is more like a punch-up in the corner of the ring and holds the attention for that very change of pace.