When Christina, Grant and their two friends join their mystery-writing Mimi (and Papa!) on a trip to the "Mile-High City" of Denver, Colorado, they soon find themselves: - Sleeping in a mysterious, haunted palace of a hotel! - Deciphering mountains of clues to solve a mystery! - Reading tattered old books to help solve the clues! - Traveling through tricky tunnels to get to a scary ski slope! - Meeting an amazing woman who once sailed on the Titanic! But can the kids have fun, stay warm and solve a mystery all at the same time? Strap on your skis and come along and see!