While a three member crew lead by Commander Melissa Lewis is out grouping samples from the Martian surface, a sudden storm creates mayhem, sweeping astronaut/ life scientist Mark away.
This causes his mates to go away him behind on the desolate planet and start their journey back to Earth, assumptive he should be killed by falling detritus. Turns out, Watney is disjointed and stranded alone on the Mars, troubled to survive with restricted resources at his disposal.
He surprisingly hopes that he might live until NASA initiates their next mission to Mars, years later.
So this is the plot around which the story revolves.