Here's an example indoors with slaved flash. In this case, 2 flashes slaved, one dominant and other lesser, both with diffusers. Since this was a mini-z and so small I shot with a Nikon 10.5 mm fisheye. Because there wasn't much ambient light, I did a much longer exposure; probably around 1/2 second and panned and panned back to try and put some of the ambient light blurs behind the car. I don't always like to use rear curtain cync since with such a long exposure I don't like losing that flash timing control. I just shoot with pan/flash/then pan backwards. a two stage pan. Example: