For a primer and story-like way to learn about this mysterious portion of the stock market, I always recommend people begin with the book Dark Pools, which was released earlier this year.
Fun With High Frequency Trading Before The "Big One" Arrives
Everyone I have heard interviewed that has an in depth knowledge or personal experience working with the high frequency trading industry says that the flash crash was only the warm up and there is a far bigger event coming. It is impossible to avoid forever based on the size and scope of HFT in the market today.
