Three bold women test their endurance and wits as they brave the formidable, migratory journey of a pregnant, scrawny doe.

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For years, researchers like Sam Dwinnell have been using GPS collars to remotely track where mule deer go and how they connect with landscapes—both wild and changed by humans. Through her research, Sam has seen how, during migration, these animals are endurance athletes—some more than others—and Deer 139 has stuck out as one of the most badass animals out there. Every year she travels 85 miles from her winter range in the sagebrush steppe outside LaBarge, Wyoming, up into and over the Wyoming Range, across raging rivers and snow fields, to an alpine cirque in the Salt River Range. As a scientist, Sam has mapped this journey but the adventurer in her didn’t want to watch from afar anymore. To see first-hand this long, complex, and until now, largely invisible journey, Sam assembled an all-woman team of naturalists, storytellers and endurance junkies to film the expedition and bring viewers along for the ride.