An enigmatic alien called Thomas Jerome Newton arrives on Earth from a drought-stricken planet in search of water to save his dying world. Disguised as a human, he leverages his advanced knowledge to patent innovative technologies, amassing great wealth. His goal is to use these resources to construct a spacecraft that will transport water back to his home planet. Along the way, he meets Mary-Lou, a naive hotel clerk who falls deeply in love with him, and Oliver Farnsworth, an attorney who becomes his trusted ally. Newton's unworldly demeanor and rapid financial successes attract attention, leading to scrutiny from government agencies and business rivals.

As Newton integrates more into human society, he encounters challenges that test his resolve and scrutiny over his mission intensifies. His relationships with Mary-Lou and Farnsworth grow increasingly complex due to his secrecy and the cultural chasm between him and humans. While trying to stay focused on his mission, Newton is confronted with human vices and distractions, like alcohol and television, which begin to erode his resolve. His once-clear purpose is blurred by emotional and existential dilemmas as he grapples with the complications of human life versus his alien origins. The stakes rise as external forces close in, further jeopardizing his mission to save his home planet, as well as his position on Earth.