Cela, a Marian colonist is kidnapped and taken to Earth.
Telesforo, and Earth-boy on an urgent mission, crash-lands on Mars.
Now both teenagers are being stalked by an unknown killer.
One thing links them. Something that will wake horrors long since forgotten. Something that will change the solar system.

Shadow of Phobos (Solar Colonies #3) by Ken Catran (soft cover, good condition)