The trail leads down from the roof, along the deck, up the siding, in through a tiny opening in the storm window, under the window sash, up the framing, onto a chair pushed up against the shutters..... ANTS!
We got a package of terro baits in the mail (thanks Charlie). I stuck one on the sill, in between the window sash and the storm window. The ants drained it and now there are one or two scavenging about, but the big trail is gone. We are waiting for it to work it's magic and destroy the colony. Keeping fingers crossed.
What do you think... set out another bait? They supposedly sell this stuff at Walgreens, Home Depot, and (gulp!) Walmart, so I'll have to check that out.