Jim Nolan is a new organizer, being shown the ropes by Mac McLeod. They become fruit pickers and jolly along a strike that is brewing because the owners have cut the fruit pickers wages. A more interesting aspect of the novel is watching Mac teach Jim how to mobilize workers through a combination of education and manipulation.
The owners respond in typical ways, using economic pressure, vigilantes, the police and the state (in the form of health regulations) to undermine the strike. The death of a worker at the hands of a vigilante galvanizes the flagging strike.
The owners then up the ante, by shooing Jim, burning buildings, and kidnapping allies of the strikers. Jim is eventually killed, sacrificing himself for his principles (or perhaps the party). Mac uses Jim’s death to further advance the interests of the workers.
-- Bob Barnetson