Gwendy's final task / Stephen King, Richard Chizmar.

When Gwendy Peterson was twelve, a stranger named Richard Farris gave her a mysterious box for safekeeping. It offered treats and vintage coins, but it was dangerous. Pushing any of its seven coloured buttons promised death and destruction. Years later, the button box re-entered Gwendy's life. A successful novelist and a rising political star, she was once more forced to deal with the temptations that the box represented - an amazing sense of wellbeing, balanced by a terrifyingly dark urge towards disaster. With the passing of time, the box has grown ever stronger and evil forces are striving to possess it. Once again, it is up to Gwendy Peterson, now a United States Senator battling the early symptoms of Alzheimer's Disease, to keep it from them. At all costs. But where can you hide something from such powerful entities?