This isn't a really old book, and I read it a few years ago. The plot is this: there are twin sisters (i think twins) one is overweight and married with children, the other is skinny and single. The married twin loses control of her car (brakes went out) and she winds up in a coma for I believe months. When she comes out of the coma, she has lost all her weight and looks like her twin now. It turns out the single twin cut the brake lines because she wanted her sisters husband and children for herself. While all this is going on there is a serial killer watching the twins, and he (or she) kills the single twin in the end. It's the beginning of a series I believe and I wanted to read the next book.
