"Racso and the Rats of NIMH" is a direct sequel to the Newbery Medal-winning book "Mrs. Frisby and the Rats of NIMH" by Jane Leslie Conly's late father, Robert C. O'Brien. Conly wrote her sequel long after O'Brien's death in 1973, so even though Conly's book attempts to answer many of the open-ended questions posed by the original, it is still Conly's work and not O'Brien's. One of the most anticipated events of the first book was the possibility of Mrs. Frisby's children (Teresa, Martin, Timothy, and Cynthia) having grown up to visit the rats themselves and partake in adventures of their own. Within this book, however, only Timothy is shown as having actually left for Thorn Valley. Teresa and Cynthia are still at home, and Martin has started a family of his own. While it ties up this plot point cleanly, many readers criticized this, feeling that the other children had much potential and deserved more exploration. Another question from the first book that Conly chose to answer relates to the fate of Justin, one of the rats who was a major character in the first book. In the end of the original story, O'Brien hints that Justin sacrificed his life when he went back to rescue a fallen rat. However, Conly chose to keep Justin alive and well in her sequel.