This article argues that The Spanish Tragedy as we know it is the second part of a two-part play; that The First Part of Ieronimo is a post-1600 revision of Kyd's genuine first part; and that one can distinguish two ‘textual layers' within the later text, corresponding to different sections of the plot. The ‘political' strand of the plot of The First Part of Ieronimo, argues Erne, has largely preserved sections of Kyd's original play. Erne reads The Spanish Tragedy as a sequel to these sections, and argues that what is generally perceived as a stand-alone masterpiece needs to be thought of—like 2 Henry IV, 2 Tamburlaine, and perhaps even Hoffman—as the second part of a two-part structure. Erne suggests that we may need to reconsider Kyd's ‘singular dramatic architecture' and his interest in complex causality.