A one-way trip through the gate, a sunken alien city, and no way to phone home. Brad Wright and Robert C. Cooper sent an international expedition to the Pegasus Galaxy in 2004 and left it there, inside the Ancients' abandoned city of Atlantis, with a power budget that keeps running out and a predator species called the Wraith stirring across the sector.

Dr. Elizabeth Weir (Torri Higginson) runs the civilian side. Major John Sheppard (Joe Flanigan) flies. David Hewlett plays Rodney McKay, the astrophysicist who is insufferable and usually right, and Rachel Luttrell's Teyla Emmagan is the local who knows what everyone else is walking into. Amanda Tapping and Robert Picardo carry roles over from the parent series.

Newcomers can start here. Atlantis lays out its own premise in the pilot and spends five seasons, 2004 to 2009 on the Sci-Fi Channel, in a galaxy SG-1 never reached, so the continuity you skip is background rather than plot. Watching Stargate SG-1 first buys you the characters' history and a sharper sense of what the Ancients left behind, though the show does not ask for it.

The register is adventure television with a sense of humour: Vancouver stands in for alien forests, the science gets waved through at speed, and the cast banters under pressure. Episodic weeks, a season arc running underneath, and a base under siege more often than anyone's nerves can take.