Turtle never told. She went to the library every Saturday afternoon, she explained (which was partly true). (28.1)
Ultimately, Turtle's the book's best secret-keeper. We defy you to find anyone who could keep a $200 million secret. Forget anyone – can you name any thirteen-year-olds with that kind of ability? Even Westing ends up sharing his most closely guarded secret – his identity – with Turtle, but only when she has successfully figured out the elaborate game of strategy he set in place to protect it. Instead, Turtle masks her lifelong lie of omission with small partial truths: she is going to a library, but it's a private one in the home of a multimillionaire, not a public building. And no one ever questions her.