Expendable Heroes: The Planet Trap. Expendable Heroes, #1

The last thing Steven remembers was waiting in a prison cell for the results of an appeals trial. His crime: speaking out against unfair treatment of workers. His opinion of his sentence: it's political. Next thing he wakes up on a commercial ship run by the Merlin Company, where he meets Luciane, Rollo and Jack, fellow prisoners of an inconveniently political nature, and the four will be sent down to a planet where a research team has vanished. Everything needed to survive and return is on the abandoned base, and all the company wants is to know what happened to twelve scientists. Except the company is lying.
They know what happened to the scientists. They're testing something, and the four are guineapigs. They're not supposed to come back. The space craft to return is not even at the base anymore. But one discovery will change everything.