In her final moments with her dying son, Sheila Blanco placed her head on his chest and made a vow.
‘It was my last promise to him,’ she recalls. ‘I said I would find out what happened at any cost.’
She little envisaged how gruelling that quest would be – and how hard it would be to fulfil it. For while Sheila has long had a very good idea of what happened in her Cambridge-educated son Mark’s last moments, she