R-T, Margaret, and the Rats of NIMH

R-T, Margaret, and the Rats of NIMH is a sequel to Mrs. Frisby and the Rats of NIMH and it continues the story after the end of Racso and the Rats of NIMH. It was written by Jane Leslie Conly, the daughter of the author for the original book.

Plot
When two children named Margaret and Artie are lost during a camping trip, they are found by the colony of rats, specifically one named Christopher. The children help the rat community with various tasks, and Artie and Christopher become very close friends. However when winter comes, the rats can't shelter the children and must send them back. The children try to keep the secret of Thorn Valley, but after pressure, Margaret ends up revealing it. The story ends with a party of adults traveling to Thorn Valley to discover the rats' colony only to discover an empty, apparently uninhabited plot of land with all traces of the colony removed. The whereabouts and fate of the rats of NIMH are left unstated, though Artie did find a gift from Christopher, a picture of an arrow, presumably pointing to the new location of the colony.

ISBN 0-06-021363-9 (1st ed.)