Gambler's World by Keith Laumer, Science Fiction, Adventure

ON THE ZOOP TOWER
It was a rigged gambling game, but Retief had to play it.
Retief was First Secretary and Consul to the Mission to the planet Petreac under Ambassador Crodfoller. The Corps Diplomatique Terrestrienne were there to help the Nenni Caste and their Potentate to deal with their rival planet Rotune.
But Retief has discovered an underground movement called The People's Anti-Fascist Freedom League headed by a fellow named Zorn.
And unless Retief and his colleague Magnan get to the bottom of Zorn's gambling operation and play their own games, a whole spaceship's worth of diplomats would get their throats cut!