Also Wilmott. Can't remember the name but it will be obvious.

It's pretty much high school math, you establish what the cash flows are and the value of the thing flows from there. When it comes to optionality you probably haven't done stochastic calculus in high school, but you can follow along anyway. Both books will explain interesting things like how to price an option on an option, that kind of thing. Non-arbitrage is what holds the the whole thing together: if the price didn't follow {rules} then you could do {steps} to make free money.