The Diamond in the Window (Hall Family Chronicles)

"As Eleanor and Edward follow the clues scratched on an attic window, they become involved in a series of dreamlike adventures that are frighteningly real and compel them to search for Prince Krishna's treasure"--

The Halls' house stood out like an exotic plant amidst all the neat, square houses in Concord. It had porches, domes and towers--and a tiny window in the attic whose raised center pane shone out like a brilliant diamond.

There had been jewels once in the house, the gift of an Indian prince to two children, Ned and Nora. The prince had devised ingenious games so that the hidden jewels could be found. And then, suddenly, mysteriously the children and Prince Krishna disappeared...

Years later, Eleanor and Eddy, niece and nephew of the lost children, set out to look for the jewels in order to save their house from being repossessed by the bank. They follow the clues of Prince Krishna's strange treasure hunt, a game harmless and exciting at first, but becoming increasingly filled with peril.

The town of Concord, with its strong literary and philosophical heritage, is the background for Langton's fantasy. Erik Blegvad's illustrations completely capture its atmosphere.