I believe a previously played Downbubble can be countered with an Upflobble.
Heathrow Airport - Terminal 4
Whoever goes next needs to be careful - I can see a possible route to Mornington Crescent two moves away....
If that's the case I'm going to have play a dangerous move an go with...
Ladbroke Grove
I think a long slow trip to PIMLICO would be in order
May I invoke the Pacific Convention and interject Waltham Cross?