Something Happened. Well, that's just it. Something happened. But we begin with a lot of questions. What happened? When did it happen? Did it happen to Slocum? To someone he knows?
Slocum offers us a series of events that have happened to him, and at first we feel like we have to pick and choose to figure out which event the title refers to. But with tension building as the novel progresses, we find that perhaps we, like the bored and complacent Slocum, are waiting for something to really happen.
The fact is that most of what goes on in Slocum's reality is soul crushing and boring. Everyone is waiting for something, anything to shake things up. People have affairs, they hope for promotions, they long to buy new houses—anything to make life seem a little less meaningless. Everybody wants something to happen.
Slocum is good at telling us about all of the things that have happened to him, as well as those things that have happened to other people. For instance, Virginia took her own life, Slocum's mother went senile, and his brother died unexpectedly. Is that what happened? He also hints that things would be better if Derek weren't around, leaving us guessing if what happens is that he eventually kills Derek.
Death is definitely the thing that happens, though what happens certainly isn't what anyone expects. Slocum spends a lot of time worrying that something might happen to his son, and sure enough, something happens to him. His son is struck by a car, and the wounds are significant. But this isn't what kills him: ironically, it's Slocum who does the deed, though with good intentions. Something happened all right—not just to Slocum's son, but also to Slocum's life as he once knew it.
And that's what happened. Tired of us saying happened yet? You'll happen to get over it, we're sure.