At the height of the War of Independence, Jimmy Mahon is given an intelligence role while Ursula Sweeney, a code-breaker with British intelligence at Dublin Castle, contemplates treason.

General Winter targets Sinn Féin's propaganda machine and their finances, while Jimmy puts pressure on Ursula to feed him information from the inside.

Distressed at the civilian death toll, Arthur returns to his family but Peggy begs him not to desert as they rely on his army pay. Charles is trapped in the Castle while his wife Vanessa discovers that he has got her guest May pregnant. Elizabeth tries to save Peter’s life when he is shot by a sniper. Frances fights alongside Jimmy as he picks off advancing British soldiers and as they flee the scene she shoots one at point-blank range. The British Army closes in on the GPO as Elizabeth breaks the news of his nephew’s death to Jimmy.

With the GPO destroyed the rebels surrender, Jimmy and Elizabeth among them. Stephen has to escort Elizabeth to prison. Charles returns home where he is powerless to prevent Vanessa from throwing May out. May is reconciled with Frances who insists she has nothing to fear as she has destroyed the stolen document. Monsignor Mulcahy breaks the news of Peter’s death to Peggy as Arthur makes for the Western Front. Harry steals money from his father. Minnie, helping in Dolly’s soup kitchen, recognises her erstwhile lover and leaves her job in shame. Stephen tries to take his own life and Jimmy and Elizabeth are separated again – both behind bars --- as the executions begin.

In the aftermath of the multiple attacks on General Winters' spy ring, the British close ranks. Elsewhere, there is a price on Ursula's head and Jimmy finally confronts the mole inside Collins' Squad.

Jimmy Mahon is moved from active service on Michael Collins' squad to an intelligence role after he's identified during an IRA hit.