Nature detective Tom Heap investigates who, or what, is killing the common sparrow.
Once one of our most common garden birds, it is now a rarity.
Since the mid-1990s, London alone has lost more than two thirds of its sparrows and there are similar cases in Bristol, Edinburgh and Dublin.
In an attempt to unravel the mystery, Tom delivers a dead sparrow to the laboratories of the Zoological Society and observes the autopsy which demonstrates that the cause of death is not always what it seems.
He speaks to experts from various conservation bodies including the RSPB and the British Trust for Ornithology to weigh the latest scientific evidence.
Tom finds out about the chief suspects, including cats, sparrowhawks, unleaded petrol, mobile phones, garden make-over programmes and loft conversions.