In this first episode, it's rush hour in the capital, and millions of Londoners are making their daily commutes. The network is close to maximum capacity with temperatures of 35 degrees above ground and much higher below. But there's also a trespasser on the line - the Emergency Response Unit must react quickly to reports of a large dog loose on the tracks underground, which has brought the Northern line to its knees. After walking through half a kilometer of underground tunnel, the ERU reach the train where the terrified German Shepherd was last spotted. The team must move fast to help sweltering onboard passengers, but rush hour delays are spreading.Above ground, it's an intensely busy day on the bus network. Picking up the slack from tube delays, Dennis and Matt are out trying to keep the service running, checking tickets and looking for fare dodgers. And at Tottenham Court Road, the scorching summer heat takes its toll as a passenger suffers from heat exhaustion. The whole network is sizzling in the heat and at the TFL Control Centre the pressure intensifies to get millions of passengers through the system.