One image that Jake Chapman is looking at depicts a sweet, grinning boy sporting a helmet made from a folded newspaper and waving a homemade wooden sword. It's the very image of the kind of wholesome, Enid Blytonesque activity that parents hope their children will be engaged in during the summer holidays but, let's be honest, probably aren't. Of course, there's a twist. The cartoon of the boy is underlaid by another drawing in the style of Philip Guston. This shows an arm holding a long serrated blade that seems to stab through the boy's grinning face into another body, spurting blood over the back of the boy's head. Nothing like this appeared amid the bonnets and bunnies of my four-year-old's Tesco Easter colouring book. Which, to my mind, is a shame.