As agents Red and Blue travel back and forth through time, altering the history of multiple universes on behalf of their warring empires, they leave each other secret messages — at first taunting, but gradually developing into flirtation then love. When Red's commanding officer detects the interaction between Red and Blue, she forces Red to send Blue a message that will kill Blue when it is read — even though she is warned of the danger, Blue reads the message anyway. After Blue is killed, Red time-travels to Blue's childhood to give her immunity to the poisoned message, which allows her to survive. This incident is discovered and Red is arrested by her own empire; Blue is then able to help facilitate Red's escape from jail and it is implied that they both are able to be free.
