This book began with a riddle. We wanted to know why a company based in a redbrick house in the English town of Rochdale was lending £2 million to two-time European champion FC Porto to sign a striker. The company listed its address as 35 Princess Street, a scruffy part of town neighbouring abandoned buildings with bricked-up windows, an advice centre for the homeless and a builder's yard. CCTV cameras pointed at the front door.

It was 2010 and the Portuguese club had recently reached the last 16 of Europe's Champions League with a squad that included Radamel Falcão, Givanildo Vieira de Sousa – better known by his nickname of Hulk – and Nicolás Otamendi. Over the next few years these three players, from Colombia, Brazil and Argentina, would subsequently fetch transfer fees totalling more than €150 million and play at some of Europe's most illustrious stadiums, including Manchester United's Old Trafford and Manchester City's Etihad Stadium, a dozen or so miles away from that ordinary Rochdale house.

As the new season got underway, Porto used the £2 million loan to help finance the signing of a striker to provide cover for Falcão and Hulk. Walter da Silva, who had been raised by his mother in a Brazilian slum, was very much an unproven talent, even if he had made his debut in Brazil's Under-20 national team a year earlier.

A second company, based in London's Chancery Lane, provided another €2 million to help finance the €6 million signing. Porto's published accounts showed ...

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