The Circles of Power

Broke, without a job, their ship almost a scrap heap, Valerian and Laureline are stuck on Rubanis, unable to pay for repairs. So when a trio of old acquaintances introduces them to the head of the local police, who is looking for independent agents for a risky - but well-paid - mission, they accept readily enough. But Rubanis is the most corrupt planet in the entire galaxy. How are they to find out who really holds the reins of power there?