After four decades of fly-by probes, orbiters, landers, and rovers, the quest for life on Mars is as tantalizing as ever. NOVA goes behind the scenes of the latest NASA missions to the Red Planet to reveal new clues and challenges on the road to answering this ultimate question. With unique access to the NASA Phoenix and Mars Exploration Rover missions, NOVA shows scientists and engineers in action, directing the operations of spacecraft millions of miles away, as the robotic explorers drill into rock, claw into soil, analyze samples, and trundle across the rock-strewn landscape in search of signs that Mars once or maybe even still harbors some form of life.