From 2153 into 2154 Enterprise searched the Delphic Expanse for the Xindi and the superweapon they were building against Earth, uncovering the Sphere Builders' manipulation behind the threat.
After the Xindi probe killed millions on Earth in 2153, Starfleet sent Enterprise into the Delphic Expanse, a dangerous region of spatial anomalies, with a detachment of MACO soldiers aboard. The crew had little more than a name and a trail of rumors to follow.
Inside the Expanse, Enterprise found that the region was being reshaped by enormous artificial spheres. It contended with hostile species, damage from the anomalies and dwindling supplies, and Archer took steps he would once have rejected, including stealing a warp coil from another ship. Gradually the crew learned that the Xindi were made up of five species and that they had been deceived into attacking Earth.
The Sphere Builders, extradimensional beings, had told the Xindi that humans would destroy them in the future. By winning over the Xindi scientist Degra and others on the Xindi Council, Archer turned part of the alliance against the weapon, and the mission ended in 2154 with the weapon destroyed and Enterprise returning to Earth.