WWII and The Girl In the Fireplace

I have a tendency to do things out of order - so I watched all four seasons of the new Dr. Who, then, realizing that season 5 of Foyles War was on order, went back and watched season 1, because I realized I'd missed it on PBS Mystery!

So I'm watching the ep. entitled A Lesson in Murder

http://en.wikipedia.org/wiki/Foyle%27s_War_Series_One#.22A_Lesson_i...

and noticed ... the Girl in the Fireplace ... was one of the lead characters ....

then I noticed a little while later a familiar face .... David Tennant is also in the ep.
I have a vague recollection that he had mentioned the two of them had been on the same show before, but hadnt any scenes together. Now I know what they're talking about.

-Don