OK, so there are three endings. That's kind of weird. However, maybe it's fitting for the game-within-a-game structure of the book. Untying such a complicated concoction takes more than one ending.
But before we talk about them more, beware: MAJOR SPOILERS AHEAD. (If you haven't finished reading the book, you might want to save this section for later! Head back to "What's up with the Title?" or check out "Quotes and Thoughts" while you finish the puzzle.)
In ending one, Turtle solves the mystery, and the other characters go about their lives. She's the winner but no one else knows it. While this might not seem like much of a prize – apart from the $200 million, that is – it suits Turtle just fine. She's good at keeping secrets, and she won the game fair and square.
Ending two takes us to peek into the characters' lives five years later, when some of them have figured everything out and some are still working on it. Everyone seems to be "growing up," though, even the adults: businesses are successful, people are getting married, and characters are seeing rewards for their good deeds.
In ending three, Turtle's with Westing when he dies for real, and she finally becomes the heir. What's most unusual about this ending, especially for a young adult book, is that we find out that several other major characters have died. The ending skips so many years ahead from when most of the game takes place that the thirteen-year-old heroine's a married businessperson. It makes sense that the book would have to get to this point, though, since the original game was tied to the "death" of Sam Westing, and the winner can't collect her prize until the inheritance becomes available.