In the wake of the 1588 destruction of the Spanish Armada, English Catholics launched an ingenious counterespionage effort to undermine the Tudor government’s anti–Catholic machinations. This Jesuit-connected network secretly transmitted intelligence to Brussels, Antwerp, Madrid and Rome. Its central figure was William Sterrell, a brilliant Oxford philosopher. Sterrell moved at the highest levels of government, working for the ill-fated Earl of Essex and for the powerful 4th Earl of Worcester, secret sponsor of the Jesuits. This is the story of Sterrell’s secret network—undetected for 400 years—brought to life in vivid detail, based on close examination of hundreds of original letters and documents never before transcribed or published.