Kate and David are eleven years old and best of friends, playing football and doing their museum project together. But in Edinburgh, where they live, time is coming unstuck and the past is breaking loose. Old Mr Flowerdew needs their help in the war between the Lords of Chaos and the Guardians of Time, centred around the mysterious Millennium Clock. But can Kate use her grandmother’s golden necklace to restrain the power of Chaos, and will David be able to help the Guardians, even if it means losing his mother all over again?