Erin loves Matt and Matt loves Kirsty and Kirsty is going out with Billy, who has a mean temper. And since Erin and Matt are sort of losers anyway, and Kirsty and Billy are popular, neither of them have much of a chance, except maybe with each other, but the games that they will play (compounded by numerous misunderstandings) ensure that everything gets pretty messed up in the end.
The story is told in two voices, shifting back and forth between Matt and Erin, and that is a clever (although not-too-original) idea. However, it is also painfully distracting. And what on earth is with these morbid British YA books where people get killed? The homicide rate in these books rival an episode of 24! Anyway, a drudgery to get through. Not worth the effort in the end.