Performance problems after combat?

[MercenaryForHire]

Here's a few snapshots from the first level of the full version. Here, I've cranked it up to 1280x1024, all details on High with the exception of Motion Blur.

In the first shot, I'm getting a buttery smooth 60fps.

In the second, I'm getting 30fps. During combat itself, it was about 20fps. That's acceptable.

In the last, I'm getting 15fps. What exactly is going on here that chews up so much horsepower?