The discovery by Enterprise NX-01 of a small derelict craft from the 31st century, and the struggle with the Suliban and Tholians who both wanted it.
The recovery of the time pod is told in the Enterprise episode Future Tense. Enterprise finds a small craft adrift with a long-dead pilot who appears human. The pod is far larger inside than outside, and Phlox finds that the pilot's ancestry includes Vulcan and several other species, a mixture that is not yet possible.
Suliban ships demand the pod, and then Tholians, in humanity's first meeting with them, do the same. Archer recognises it as a relic of the Temporal Cold War. As Trip Tucker and Malcolm Reed study it they are caught in repeating moments of time.
The Tholians disable the Vulcan ship sent to collect the pod and defeat the Suliban. Archer has a beacon aboard activated, and the pod and its pilot vanish, apparently recalled to their own century.