Acclaimed art historian Andrew Graham-Dixon gets hands-on with history as he joins with members and employees of the National Trust in discovering the secret life of a country house. Every autumn, the Trust puts its 300 houses 'to bed', but it's far from a time for rest. What happens after the visitors have gone is the biggest spring clean in the world, requiring not just hard labour, but delicate hands and an in-depth knowledge of conservation science. Shut off from sunlight and working in almost freezing conditions, Andrew discovers exactly what it takes to preserve much of our national heritage. The dust that gathers, the damp that creeps, the bugs that hide, the bats that nest, the gardens that prosper, the bits that break, the clocks that stop, the paint that cracks, the marble that chips – the magic that happens under cloak of darkness in these winter months is a miracle to behold. From a Turner painting to a rare Roman statue, Andrew Graham-Dixon rolls up his sleeves and commences a unique voyage of discovery as Petworth House undergoes The Big Spring Clean.