Episode 52 of "Stargate Atlantis"
s03e12 Echoes

When McKay finds his “whale” circling the floating city, strange events begin to occur. Teyla begins to see people that aren’t there. Then Weir begins to see the same people too. Soon everyone begins to see visions of Ancients who appear to be in distress. Can the arrival of McKay’s whale be connected to these visions? Can the visions the team are seeing forebode an impending event? Also, can the team make sense of the weird voices they are hearing during their visions, in order to understand the unknown danger in front of them? McKay’s answer leads to a daring plan by Sheppard that might just possibly save all the biological life on the planet.