Colin and Nevaeh, whose parents own rival junk-removal businesses, uncover mysteries hidden in attics and basements and discover how trash can become treasure. In The Secret Letters, Colin and Nevaeh find vintage letters that lead to interlocking mysteries from the 1970s and '80s, and they learn about "women's lib," the ERA, and other social issues from that time in history—and the way echoes from that era affect Colin and Nevaeh themselves. When Colin finds a shoebox full of letters hidden in a stranger's attic, he knows he's supposed to throw them away. That's his summer job, getting rid of junk. But Colin wants to rescue the letters—and find out what really happened to best friends Rosemary and Toby way back in the 1970s. Meanwhile, across town, Nevaeh also finds a mysterious letter. But this one reads like a confession to a crime. And Nevaeh knows her father, the "Junk King," expects her to join the rest of the family in blaming a single suspect: his business rival, Colin's mom. But that's not what Nevaeh wants, either. Even as one set of letters bring Colin and Nevaeh together, the one Nevaeh found threatens to tear them apart. Is their new friendship as doomed as Rosemary and Toby's? Each book in the Mysteries of Trash and Treasure series will examine a different time period in history and make readers think about how we value the stuff we hold on to—and what it is that makes it valuable.

New York Times bestselling middle-grade thriller author Margaret Peterson Haddix returns to the Mysteries of Trash and Treasure series as Colin and Nevaeh unravel a mystery from the 1930s and explore the emotions associated with death and dying. Colin and Nevaeh are great at finding things. After all, they found each other and became best friends—even though their parents are business rivals. They also found hidden boxes of secret letters, which led them to unravel mysteries about kids from the 1970s. But when they started Mystery Solvers Inc., they didn’t expect to be asked to find a ghost. Ree recruits them to investigate a series of old, spooky photos left behind in her family’s new house. The photos show a boy who looks totally see-through. And in some, he’s in a coffin. That’s not so odd for Ree, who lives above a funeral home. But when Colin and Nevaeh start investigating, they discover other sightings of the boy—and other secrets Ree is hiding. The more clues they find, the more they realize this mystery goes back to a time called the Great Depression. Will history, once again, help them solve the case?

Colin has spent all summer solving mysteries with his friend Nevaeh. But they’ve only ever dealt with other people’s mysteries—ones that are safe for Colin to think about. He’s still stuck on the mystery surrounding his own father, who his mother refuses to talk about and he can’t remember meeting. Then one morning Colin finds a shoebox on his porch with a note on top: “Your father wanted you to have this.” Inside the box is a key. This new clue makes Colin even more determined to find out the truth about his dad and why his parents split up when he was a baby. Colin and Nevaeh begin investigating Colin’s father in a quest that takes them from eerie storage units to lock-lined bridges to, strangely, secrets in Nevaeh’s family. But the closer they get to connecting the clues, the more trouble awaits them. A serious accident leaves Nevaeh’s family reeling—and Nevaeh racked with guilt. And digging into Colin’s father’s past may lead Colin and his mom into even more danger. Can Colin and Nevaeh solve the mystery before it's too late?