The Poldarks look forward to life together in peace, but a plea from his old army colonel, Ned Despard, compels Ross to the capital. Arriving in London, he finds a city gripped with paranoia, and is determined to save Ned from the conspiracy that imprisoned him.

As George expands his power through a shady alliance, the Poldarks become caught in a deadly web.

Ross's tenacity in helping Ned bears fruit, but not without cost. Hanson’s presence in Cornwall raises suspicion and as Demelza wrestles with how best to equip the community to look after itself, Morwenna lends herself to the cause and finds new hope.

Ralph seeks to ruin Ned as rebellion stirs and the Poldarks are trapped in the middle.

George’s cabal moves to ruin the Poldarks, and Morwenna wrestles with a heavy decision.

Ross discovers a French plot, and George finds himself at the mercy of Joseph and Ralph.

With the fate of his nation in the balance, Ross must gamble everything to protect his country and those he loves.