A woman managed to steal £4.2 million worth of diamonds, equivalent to around $5.7 million, by posing as a gemologist and replacing the valuable stones with regular garden pebbles.

The elaborate heist took place at the Boodles showroom on New Bond Street in Mayfair, central London. According to The Guardian, Lulu Lakatos allegedly pretended to be examining seven diamonds in the showroom but actually swapped them out for pebbles before leaving. It wasn’t until Boodles’ own diamond expert went and examined the bag where the diamonds were kept that they noticed they were robbed. 

Prosecutors made the claims in court on Tuesday.

According to prosecutor Philip Stott, Lakatos was able to snag the diamonds with a sleight of hand before anyone noticed.

“The diamonds had been stolen by the defendant by sleight of hand,” he said. “The conspiracy in which she is alleged to have played an integral and central part was one of the highest possible sophistication, planning, risk and reward.”