This Josiah Crabtree had once sought to marry Mrs.
Stanhope, thinking thereby to get control of her money and the money she held in trust for Dora.

The lady was weak and sickly, and the teacher had tried to hypnotize her into getting married, and had nearly succeeded, but the plot was nipped in the bud by the Rover boys.
Tad Sobber met Josiah Crabtree and the pair hatched out another plot, this time to abduct Mrs.Stanhope, getting the lady at the time to bring a good share of the treasure with her under the impression that it was to be invested by her friends.

The lady was carried off to an island in Casco Bay, off the coast of Maine, and thither the Rover boys and some others followed them.

There was a good deal of excitement; but in the end the lady was rescued and the treasure brought back.

An effort was made to capture Tad Sobber and Josiah Crabtree, but the two evildoers managed to get away.
The home-coming of the boys with Mrs.Stanhope had been a time of great rejoicing.