Zelenka: Pigeons.
McKay: Are affected by the tiniest anomalies in the magnetosphere. It's as if their internal compasses were somehow, well... pigeons?
Zelenka: Yeah, homing pigeons. I used to raise them before coming here. We used to consult solar charts before our pigeon races.
McKay: Pigeon races?
Rodney's old friend Sam the Whale has been spotted circling Atlantis. Why is he called Sam? Because "it's a boy's name too." Actually, Sam is not a whale, but a large species of fish called a Flagecallus by the Ancients — but we all know a Space Whale when we see one, so "whales" it is. And there sure do seem to be a whole heck of a lot of them. Sam is joined first by his mom, then by a few more pods, then by what seems like every freakin whale on the planet. Sheppard wonders if they make good eating.
Meanwhile, people around the city start seeing flashes — an ancient woman speaking gibberish, a burned man in a pilot's uniform. Teyla thinks they might be the ghosts of the slaughtered Ancients from the last couple of episodes. Ronon thinks they're the product of too much meditation. McKay manages to figure out that they (along with headaches and nosebleeds for everyone) are caused by the whales singing at them.
Fortunately, the city just happens to come with a whale-song-decoder! The whales are replaying events that happened 15,000 years ago, stored in their genetic memories. It's a warning. The Lantean sun puts forth a massive coronal emission every — you guessed it — 15,000 years. Last time, the Ancients got warning and were able to extend their shield to protect much of the planet, but it was still a Mass Extinction Event with respect to the unprotected area. Those, of course, were shields powered by three ZPMs — after giving one to the SGC to power the Antarctic base and one to the Odyssey to help in the fight against the Ori, Atlantis only has one of the Asuran ZPMs left, not nearly enough to protect the planet.
The only option is to stop the coronal mass emission in its tracks. That is to say, fly the Daedalus up really close to the sun, boost its shields with the ZPM, and deflect the jet of hot plasma around it so that it misses the planet. Fortunately, these things don't last very long. The Daedalus gets a little toasted, but the planet is saved, and the whales return to doing whatever it is whales do.
Notably, this is the first episode in the show in which the major problem was in no way caused or exacerbated by the expedition itself.
Tropes
- Apocalypse How: Class 4. Zelenka says that past coronal mass ejections and the Atlantis shield explain the evidence of mass extinctions he's seen far from the city.
- Brown Note: The visions of past Lanteans the Atlantis team experience are due to subsonic communications from the "whales" based on their collective Genetic Memory. Unfortunately, the low-frequency echolocation calls and EM fields they generate are also harmful to humans, so the whales inadvertently kill one person and cause serious though not irreparable damage to many others.
- Continuity Overlap: Weir mentions the Ori Crusade as part of the SGC's justification for taking two of the Asuran Zero Point Modules and installing them in the Antarctic Outpost and the Odyssey. With this episode taking place just after the events of the SG-1 mid-Season duology "The Quest" and the Ori obtaining the Sangraal, it's completely justified the SGC would be seizing any advantage they can against the Crusade.
- Convection, Schmonvection: Averted. While the Daedalus shield deflects the CME, there is residual heat buildup that starts damaging the hull as the CME progresses.
- Deflector Shields: The Daedalus's Asgard shields (boosted by an Ancient ZPM) are able to withstand a point blank coronal mass ejection from the Lantean sun.
- Didn't Think This Through: Sheppard's so focused on the 'Use the Daedalus Shield to Deflect the CME' plan that he doesn't think to ask Rodney exactly how long a CME actually lasts (such as up to several hours). Of course, Rodney's not exactly blameless here either. Even though Rodney knows all this, he doesn't explain it to Sheppard while trying to dissuade him from the plan — something that a pissed-off John calls him out for once he realizes the plan's in trouble.
- Genetic Memory: Now with instant playback capabilities.
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Never Live It Down: The look on Weir's face when she realizes Rodney was Properly Paranoid about keeping all three ZPMs after all. It just screams, "I'm never going to hear the end of it from this Canadian." - Not Listening to Me, Are You?: Before McKay's hearing has recovered, Sheppard tries to get his attention:Sheppard: Rodney! Canadian Football League's a joke! Céline Dion is overrated! Zelenka is smarter than you are! [Rodney mentions an Ancient biolab and suggests checking it out] OK, Meredith.
- Properly Paranoid: The episode starts out with McKay objecting to two of Atlantis's ZPMs being sent elsewhere (Antarctica and Odyssey). At the time Weir correctly points out that the power sources are badly needed in those places; later of course it turns out that Atlantis is facing an imminent and lethal crisis which could have been easily solved if all three ZPMs were present. McKay wastes no time pointing out that he was correct.
- Sequel Episode: To Season Two's "Grace Under Pressure".
- Status Quo Is God: Atlantis is back to one ZPM after burning the last one out several episodes ago and then getting three from the Asurans.
