'MobLand' Episode 7 Ending Explained — Who is Kat?

In a shocking twist in MobLand Episode 7, Harry (Tom Hardy) calls in a very big favor in order to get the Harrigans out of one very particular jam. But who is this mysterious new character? And how will she impact the second half of the show? 

Here's what we know about Janet McTeer's formidable Kat McCallister, plus why the ending of Episode 7 seems to hint that Harry is playing a bigger game than we ever suspected. Spoilers ahead.

MobLand Episode 7, Ending Explained 

In the final moments of Episode 7...