In 1788, Lieutenant Daniel Rooke sails into Sydney Cove with the First Fleet, hoping to advance his career. Instead, his life is unimaginably changed.

As a young officer and a man of science, the eccentric Rooke is full of anticipation about the natural wonders he might discover in this strange new land. As the newcomers struggle to establish a settlement for themselves and their cargo of convicts, Rooke sets up his observatory to chart the stars.

A young Aboriginal girl visits and begins to teach him her language. As they learn to speak together, they build a rapport that bridges the gap between their dangerously different worlds. Then Rooke is given a command that forces him to choose between his duty as a soldier and the friendship that's become so precious to him.

The Lieutenant charts a unique moment when one world engaged with another, leaving both changed forever.