(3x14) Light of the Foundation: Part 2, Episode 2
As battle mounts it looks like humanity might stand a fighting chance, though the size of the alien army beyond the wormhole is still undetermined. Scans reveal to everyone's satisfaction that no alien ships have yet reached the inner solar system, and much to Metis' excitement, the back lines begin to converge toward the portal until a clear battlefront is established surrounding the portal at a distance in the outer reaches of the solar system.
Then, into that battlefield, a wrench is thrown as an enormous unidentified ship enters the system not through the eye but from open space, at nigh-luminal velocities, and rapidly decelerates. Thinking it aligned with the aliens, the forces of humanity scramble to reorganize their defense, concentrating the bulk of their fire on this ship that seems large enough to just wade through their defensive line soaking up damage. Meanwhile, strategists scramble to figure out the implications of the aliens having already sent a ship at nigh-luminal speeds through open space toward Sol some unknown generations in the past, long before Luke and his Horsemen even opened the portal, and whether that might make sealing off the portal ultimately futile if this is just the point ship of a fleet already en route.
Everyone grows even more confused when it's realized that the alien fleet they were already fighting are themselves firing on the newcomer ship as well. Shortly thereafter, the newcomer ship broadcasts a message encoded with a Foundation key: it is the Einherjar, the former crew of the Valhalla.
Next: Light of the Foundation: Part 2, Episode 3