Karen McManus’s debut thriller, One of Us Is Lying, was a runaway hit, spending months on the bestseller list and winning countless readers with its twisting storyline and addictive elevator pitch: Breakfast Club with murder. Now she’s back with a bestselling sophomore novel, Two Can Keep a Secret, a cold case mystery set in the tiny town of Echo Ridge. We talked to McManus about the new book, plotting a sprawling story, and how she finds time to write.