Recently let out of prison, the Tom Joad hitch-hikes his way back to his parents house in Kansas (or some similar dust bowl state), only to find that it was abandoned months ago. Along the way he meets an ex-preacher who points him towards his Uncle John's house a few miles away.
When Tom and Casey (the ex-preacher) arrive at Uncle John's they discover that the entire family was moving out to California in search of work because they found a flyer advertising fruit picking jobs. They get a shitty truck and move west with all their shit. On the way they stop at many Hoovervilles and see other families forced to migrate west. It sucks for them because the grandpa and grandma die, Tom's retard brother runs away, Rose of Sharon is pregnant and then gets left by her fiancÃ©. They get to California after taking a lot of shit from cops because they were quite prejudiced against "oakies", the derogatory term for those mid-western folk who had to pack up and move west. The California folk didn't like 'em much because they was takin' all the jobs and doin' them for less and less, competing for lower wages just to get the shitty job.
After being in a work-camp type community in California for a while, some rabble-rousing, oakie hatin' California guys chase Tom and Casey. Casey gets smashed in the temple with the blunt end of a pick-axe and dies. Tom in turn kills one of their pursuers and is hit in the face with a shovel, funs away, and is forced into hiding because if any of guards saw his face, they would know it was Tom who killed the guy.
The Joads flee the pickin' job for a different one miles away. They live in old rail cars with other worker's families and Tom has to hide out in a hole in the dirt. The Joad family picks cotton all day long, then Ma sneaks away to give Tom a bit of dinner. This goes on for a while until Tom's little sister tells a kid she was fighting with that his brother killed a man and is hiding now. Not wanting to take a chance, Ma visits Tom in his literal man-cave and gives him $50 dollars to go on the run.
Shortly after Tom's departure, Rose of Sharon goes into labor and shits out a dead-ass baby corpse. She is sad. Then there is a massive storm and the Joads find refuge in an old abandoned barn only to find this homeless guy and some boy huddled in the corner. I think the man was sick or something, and with no food to be had, Rose of Sharon whips out her tits and breast-feeds the hungry grown man, using the milk that would have sustained her own baby's life to nourish a stranger in need.
There's a lot more to the story, but I wanted to keep it short.
Seriously, though you should just fucking read it because it's a great book.