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.