Michael Pearce's tenth irresistible adventure for Colonial Egypt's the Mamur Zapt is fresh, funny, and "Still as fertile as your favourite oasis." Inevitably, as the tide of Nationalism sweeps the British Protectorate towards the realities of the dawning Twentieth Century, New Egypt is eroding the ways of the Old. But, as Gareth Owen, head of Cairo's Secret Police well knows, "The Old Egypt had a habit of rising up every so often and giving the New an almighty kick in the teeth."It's called the Tree of the Virgin. It's a sycamore, actually, not the English sort but the Egyptian, a species of fig. The tree is a site of religious interest, said to be a spot where the Virgin Mary hid herself from Herod's soldiers in its branches. Or perhaps the Virgin and Child rested there on their flight into Egypt. Whatever, it's perilously close to the gash being cut for the new electric railway running out of Cairo to the New Helipolis being built in the suburbs. Sinister power groups are jostling fo