One windy, November day, a cry for help comes into the Coast Guard Station in St. Ignace, Michigan. A plane has crashed on Mackinac Island and it's up to The Guardians of the Straits to answer the call. The Coasties quickly rush to their motor lifeboat, along with their newest and most fearless crewmember, Onyx the dog, leading the way. After a harrowing boat ride in gale winds and dangerously high waves, the Coasties still have to fight their way through the debris on the island to look for survivors. What they find in the wreckage surprises everyone but Onyx, who proves to be a hero once again.