When Suki digs up an old bone tool covered with markings, Molly, Tooey, and Oscar discover the playful pooch has made an important archeological discovery. Then, Molly announces a contest to design an original flag for the Denali Trading Post inspired by Benny Benson, the real-life Alaska Native boy who designed the state flag of Alaska.
It's a cold winter and Molly is set on discovering a hot springs Grandpa Nat once found in a blizzard, so she sets off with Grandpa, Dad, and Tooey on two snowmobiles and with a list of vague directions. Then, Tooey's hero, dog musher Eugene Pike, is recreating a historic mail run across interior Alaska. When ice breakup at the river threatens Pike's progress to Qyah, it's up to Tooey and Molly to help him finish the mail run.
Molly retells the story of the summer Trini moved to Qyah from Texas, and how she and Tooey attempted to make Trini feel at home - with cowboy hats, lassos, and 'yee-haws.' Then, Molly flies north to surprise Nina with a hand-delivered party box of goodies (and herself) for Nina's birthday, but her plans are jeopardized by a moose blocking the runway.
Molly can't wait to catch her first fish (and to earn her own first fish tale), but when she gets to the river, the only thing she catches is Tooey's missing boot. Molly must put her knowledge of the salmon life cycle to the test and find out where the fish are before the day is through. Then, Molly suggests a community fun-raiser to fix her school roof after a snow storm. The main attraction? A giant maze made of snow. All is well until Trini gets lost in the maze and Molly realizes the maze map is out of date. Can Molly and Tooey find a way to help Trini escape the maze?