Cousins William and Maxine think they are going to be spending the Summer of 1929 on a boring visit with a grandfather they have never met. They quickly find out that he is not your average grandfather.
The two of them are swept up in an adventure that has them wandering through the streets of New York trying to find and rescue their grandfather from strange, foreign and deadly men called the Hashashin who work for a mysterious, Old Man on the Mountain. The Old Man wants to obtain an elusive and magical treasure, The Eye of Midnight.
While trying to rescue their relative, the children realize they are stronger and braver then they ever imagined, and they are amazed at the secrets that are revealed!