Onyx and Hogan are ready for another adventure, but this time they aren't on a mission to save lives, they're on a mission to save Christmas! Once a year the Mighty Mackinaw becomes the Christmas Tree Ship, delivering trees to families in Chicago who might otherwise have to go without a Christmas tree. This year Onyx and Hogan are along for the ride! But as the 240-foot Coast Guard cutter is delayed due to the thick ice of Lake Michigan, Onyx and Hogan grow concerned. And as the cold temperatures continue to drop, the families waiting at Navy Pier worry the ship might not make it. Will they have to go without a tree this Christmas? A holiday story like no other, and sure to become a family favorite.