ExposureHELEN DUNMORE (HUTCHINSON, 391 PP, £16.99)Tablet bookshop price £15.30• Tel 01420 592974 It’s the height of the Cold War, 1960 to be precise, and a hunt is on for a mole in the Admiralty. A file goes missing and so does louche old Giles. Simon, a young middle-ranking colleague, suspects his old friend Giles – but the two of them go way back, to when Simon and Giles were more than just friends. So are we talking spy fiction here? The painstaking unpacking of a chain of events that leads to the exposure of the spy? No. Helen Dunmore is not John le Carré. Her new novel is just as thrilling, just as unputdownable as any le Carré, but the unmasking of the spy is not the point. The reader knows the identity of the spy almost from the off.What