Officers were called at about 10.10am to the collision in Drove Road, involving 2 cars and 2 pedestrians.
Pedestrian, Martin Harker,68, of Green Acres, Sandy, suffered fatal injuries and died at the scene.
A young boy, also a pedestrian, was flown to Addenbrooke's Hospital in Cambridge, by air ambulance ,where he remains in a critical condition.
The driver of one of the vehicles was also taken to Addenbrooke's Hospital ,with non-life threatening injuries.
Anyone who witnessed the collision is asked to telephone PC John Blood from the Roads Policing Unit on 101.
E&OE google.com/+JulianBray Tel:+44 (0) 1733 345581 .