It is Halloween and in the control room, B watch are on duty and expecting a busy night. A call from the London Fire Brigade requesting assistance at a fire in a block of flats immediately puts the team under pressure. Crewmates Sarah and David are dispatched, joining 106 other emergency services personnel at the scene. Mother-and-daughter team Nicola and Maisie have just finished with their first patient of the night but are immediately dispatched to a 12-year-old boy who has had an unfortunate accident. As the night shift continues, multiple 999 calls flood in reporting a devastating scene after two buses and a car have collided. With multiple casualties, the situation is declared a significant incident. This is rare occurrence - London Ambulance Service have only declared this twice in the last year. On this busy Halloween night, the service must somehow make ten more ambulances available at the incident. Nicola and Maisie are amongst those sent to help.