After a lot of rain, water stain on inside wall in hall!

[Mopsy]

I have a dormer bungalow with a feature high ceiling hallway. In the corner, aligned with lead flashing and guttering on the outside, I noticed a small wet patch today. Builder is calling tomorrow to look at it.

Just wondering, IS it the flashing or gutters? Although the gutters are quite free. I noticed looking at the "area" on the outside, that there are two "bubbles" on the flashing? Anybody got any ideas?

Hope it is nothing serious. House is 11 years old.

Thanks.