Battersea, 1985. Four school mates. BMX bikes. rhyming slang, Saturday football, TV nights, Doctor Who, The Goodies, Grange Hill, Madness on vinyl and the occasional blown Walnut Whip and Buster the Terrier.

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Billy, Jack, Harry and Sam know Battersea inside out - the shortcuts through the park, the streets around the Power Station and every corner worth exploring.

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Then Billy’s grandad innocently produces an old map from a work diary showing a forgotten steam tunnel beneath the Thames and everything else stops.

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With Buster the terrier at their heels, the Battersea Boys set out to find the tunnel and discover what has been hidden beneath London for decades. Some secrets never stay hidden.