The lights on the Tube carriage flicker on and off.
Outside, the occasional spark is visible. The rattling as it makes its way along the Circle Line is soothing; it's rhythm easing the passengers into a false sense of security. 7/7 panic has subsided, everything will be OK.
So why has the train now stopped? No word from the driver. People are getting nervous, fidgeting in their seats. Don't make eye contact with anyone.
A noise, outside.
The rumbling starts quietly but gets louder. Nearer. It feels almost like an earthquake...but we don't get earthquakes in central London. Do we?