The Number Sheet Puzzle is the first book in The Mason Trio Math Mysteries Series. It involves two brothers and a sister who attempt to solve mysteries by using their mathematical skills. With their parents away on their twenty-fifth anniversary trip, the trio is left alone for the summer. Susie Mason tells her brothers, Mark and Jeff, about this research she has been doing regarding a bank robbery in New York City. Knowing that Mark has a love for mysteries, they decide to look into this robbery in more detail. The three decide to investigate the bank robbery more and go to New York City not knowing the danger they may facea]They discover that in solving this robbery they will have to use their deductive skills to determine the location of the stolen money and come face to face with an armed criminal.