What I Saw and How I Lied is an incredibly straightforward title that basically describes the whole plot of the story. Evie comes to see the truth about her family's vacation to Palm Beach—that her mom carried on an affair the whole time, that Joe stole money from dead Jewish families during the war, and that Joe and Bev were probably complicit in Peter Coleridge's death—and she ends up lying about it all to cover for her parents.
Plus the book reads like a sort of catalogue of what Evie sees—and as her eyes open to the world around her and how it works, she sees more and more. For more on this, hop on over to our analysis of the book's tone in the, well, "Tone" section (go figure).