Stargate Atlantis: Season 3, Episode 12

3 - 12: Echoes

Teyla begins to see apparitions of ancients in distress and believes they are the ghosts of the Ancients recently massacred by the Replicators. Meanwhile Rodney McKay believes he's found the whale that saved him a year ago while trapped in a submerged puddle jumper. But while taking a jumper out with Col. John Sheppard to investigate his old friend they discover the whale is not alone but is one of dozens of its kind, all headed directly to Atlantis.