Advanced - Intrigue at the National Gallery of London

The tip-off? It had come from an old landline in the basement of the National Gallery, so the caller could have been anyone associated with the institute, and possibly even the director himself. But finding out exactly who had made that call was proving more troublesome than Inspector Zhang had anticipated, since the phone had been wiped clean of prints, and none of the staff - even when questioned privately - showed anything but bewilderment at any suggestion of impropriety.

So who had snuck into that backroom, and was there any substance to their allegations of artistic skullduggery? Complicating matters further was the demand for extreme discretion coming down from his supervisors at Scotland Yard, who themselves were now under pressure from Downing Street and the House of Windsor, both parties well aware that with the integrity of the Royal Collection at stake, the nation itself might face a public scandal that could threaten the integrity of the monarchy itself.