The saddest part of rereading this play for the first time in about 20 years is that it doesn't include the fantastic speech by Alec Baldwin from the film. I bet I had the exact same thought when I read it the first time. I saw the movie when I was like 12 and well, I can't say I really understood what was happening, and especially what "leads" were, but I liked a lot of what I was seeing. It's one of those movies where you can just tell a bunch of actors are acting the shit out of things.
The play is based on David Mamet's experiences as a salesman in the late 1960s. And I am sorry if you are in sales, but it just seems like the most miserable job in the world to me. It is often filled with some real... well, characters. The play is set on the day of a sales contest, where the top salesman of the day will receive a bonus. There's a sense of desperation going around the office. Things are dire for Shelley, an older salesman who used to be very successful but is now in a slump. They're also bad for Moss and Aaranow, who believe things are being divided evenly in the office. So they hatch a plan to rob the office, taking the leads and anything else of value and selling it to a competitor. A final thread in the play is Ricky Roma, the best salesman in the company. He is closing in on a sale but has to deal with a customer's hesitation. Central to all of this is John Williamson, the office manager whose job is to distribute the leads according to the directives from his superiors.