More info at this link: http://weblogs.variety.com/on_the_air/2010/06/torchwood.html

Highlights:

Davies said the upcoming season of "Torchwood" involves a global crisis, "but always being handled with a lot of wit and a lot of truth and a lot of darkness...The coming season will contain a story arc that comes to full completion at season's end. It will pick up after "Children of Earth" left off, but in a fashion that doesn't require new viewers to have knowledge of previous episodes, he said. ...

In addition to John Barrowman's Capt. Jack Harkness and Eve Myles' Gwen Cooper (pictured above), there will be two other series regulars and a host of recurring characters.

And finally, for those of us worried that he'd keep killing off main characters, it doesn't sound good:

As evidenced by the tumult of "Children of Earth," "Torchwood" isn't exactly a show afraid of confrontation and change, and above all, that's what Davies hopes will continue forward.