The Magpie is the second Spy Hunt memory of the World War I simulation: a spy held in the Tower of London has been telling anyone who listens about the Assassins, and Churchill offers Lydia Frye the chance to silence him. Best done by getting the guards to kill him.
Part 6 of 7 in World War I
Churchill treats this one as a favour to Lydia: the prisoner keeps talking about a Brotherhood of Assassins, and she may want him quiet before it causes her trouble.
Get into the Tower of London. In a side building you find a dead guard, which tells you the Magpie has already broken out. Track him down and kill him; letting the Tower's own soldiers do it earns full sync.
By the war the Tower of London was back in use: the British Army trained soldiers there and held prisoners of war. Its database entry notes that twelve German spies were shot by firing squad at the Tower in 1914 and 1915.
The full-sync goal is for the Tower's soldiers to kill the Magpie, not Lydia. Once you pick up his trail after the escape, draw the fight toward the guards and let them finish him instead of using the Hidden Blade.
The other spies threaten Britain; this one threatens the Assassins. Churchill hands him over as a gift and warns he could cause trouble for Lydia's associates, which shows Churchill knows about the Brotherhood and is willing to help keep it hidden.
The Apothecary Twins
The Apothecary Twins is the first Spy Hunt memory in the World War I simulation: Churchill sends Lydia Frye after a spy posing as a nurse who collects blood samples, and her brother who supplies her drugs. You spot their meeting and kill both.
The Darkest Hour
The Darkest Hour is the first World War I memory: as Lydia Frye in September 1916, you clear German spies from a safehouse, find a hidden radio guiding zeppelins inside Tower Bridge, then man an anti-aircraft gun on a boat to bring down the raid's escorts.
The Master Spy
The Master Spy is the final memory of the World War I simulation: Lydia Frye leads Churchill's men against the spy ring's headquarters in a carpenter's shop, chases the ringleader when he escapes, and finally assassinates him.
17 Walpole Lane
17 Walpole Lane is the last Spy Hideout memory in the World War I simulation. Lydia Frye raids a house run by a cross-loving new tenant and his hired thugs, takes the spies' documents and frees two captured allies.