This essay takes a diachronic and phenomenological approach to the ending of Seneca’s Medea and pursues the semantic possibilities and consequences of Seneca’s choice to separate the murders of the two children. I look first at the development of Medea’s character throughout the play: What might an audience think drives this Medea to filicide, and how does Medea’s speech specifically guide the audience’s expectation of the ending, despite the fact that her decision to kill the children is only explicitly stated in the final act? Then, focusing on the final act, I argue that the interruption of Medea’s murders by the arrival of Jason and the Corinthians provides an interstitial space in which the audience might not only contemplate alternate outcomes—for example, perhaps this Medea will choose not to kill the second child—but also heighten their awareness of their own expectations of the plot and of the Medea character. I show that the space between the two deaths allows for several shifts within and outside of the play: the unfixed ending of the manuscript tradition shows the breadth of viable outcomes (and the discomfort of more modern editors with non-canonical endings). Seneca’s Medea, due to the interruption, changes the significance of the second child’s death such that it is quite distinct from the first; and Jason and the audience experience their own ‘becoming’ as Medea claims the life of the second child and flies away.