The mystery in The Westing Game is who killed Sam Westing.
The Westing Game is focused on identifying the person who killed Sam Westing. The heirs are paired into teams, and each is given $10,000. They are also given cryptic clues that lead them on the chase.
In his will Sam Westing implied … that (1) he was murdered, (2) the murderer was one of the heirs, (3) he alone knew the name of the murderer, and (4) the name of the murderer was the answer to the game. (ch 8, p. 47)
The pairs argue and accuse, but eventually work together. There are several red herrings, or clues that throw the reader off track. One example is the bombings and another is the thefts. In the end, Turtle realizes that Sam Westing is not really dead, but in disguise as the doorman, and she wins the game.