In one man's mind, the alien invasion has already begun... Professor Paul Cameron is the only one who can hear them, the voices in his mind, sinister and menacing. At first he believes that they are only delusions. But the truth is far more disturbing--somehow, Cameron is able to hear Martian spies conferring telepathically. Their ominous plotting is terrifying enough, until the moment they realize someone has been listening in... The aliens attack Cameron's mind with commands to kill himself, terrible orders he is barely able to resist. When an alien-possessed human murders a witness to the latest attempt on Cameron's life, he realizes they are more powerful than even he imagined. The extraterrestrials can invade human bodies, as well as minds, but they have an even bigger target in sight: Earth. Cameron must stop them, but with their parasitic abilities, the enemy could be anyone--from the alluring student who is trying to seduce Cameron, to her jealous boyfriend, the skeptical university colleague, to the unassuming stranger at the local diner. As Cameron desperately searches for answers, he holds the fate of mankind in his hands. But will anybody believe his warnings?