Stunned by the death of former Starfleet rival and friend, A.G. Robinson, in a mountain climbing accident, Archer grudgingly recalls their competitive relationship with T'Pol as they probe a possible dark matter nebula during a shuttle voyage. He describes how he and A.G. broke the Warp 2.5 barrier on the first high-warp test flight that saved the NX program almost ten years earlier. After they confirm the first dark matter nebula, T'Pol suggests Archer name it the Robinson Nebula.

The Xindi, an alien race from the Delphic Expanse, launched a devastating attack on Earth, causing millions of casualties and massive damage in Florida. As Enterprise returns home, an unlikely source from the future informs Archer about the Xindi and that their next attack will destroy Earth. Capt. Archer and the crew embark on a mission to the galaxy's far reaches to stop the Xindi. Complicating matters are the machinations of a vengeful Klingon still looking to capture Archer.