Sierra is pretty excited when she discovers on her fifteenth birthday that her best friend from NASA Space Camp has moved from Australia to live near her in California...but she has no idea just how exciting - and dangerous - things are about to become. David and Sierra are recruited by NASA for a mission to Mars. A last, desperate attempt to unlock the secrets of Martian civilisation before the planet is destroyed by a giant asteroid. Training to be astronauts and taking the trip to the International Space Station alongside experienced pilots is challenging enough, but time is short and the teenagers will have to undertake the perilous Mars exploration alone. They knew the risks when they accepted the mission - but when their only landing craft is seriously damaged, they have to face the possibility that they may not survive this adventure...