?One of the Rose bay Willow herbs perhaps?

I'm waiting for the other shoe to drop!

Doesn't look like a willow herb to me... can we see a photo of the whole plant or is that it in the 2nd pix? I take it the first pix is the roots...

I think it's Hairy Willowherb.
Take a look at this page, it shows the roots.

http://www.kingcounty.gov/services/environment/animals-and-plants/noxious-weeds/weed-identification/hairy-willowherb.aspx

Could be...

It's Epilobium hirsutum, Great Willowherb. Impressive roots! Although the flowers are large and attractive, it's invasive. One to be rid of in the garden!

That's the same as the one I said - Hairy Willowherb, Great Willowherb, Great Hairy Willowherb, they are all different names for the same plant - Epilobium hirsutum :)