Police raided an abandoned former Boots store - only to discover hundreds of cannabis plants inside. They burst into the building in Burslem, Stoke-on-Trent, on July 4.
Staffordshire Police are now trying to find the gardeners and brains behind the mass operation, Stoke-on-Trent Live reports.
A police spokesman said: "We are investigating after approximately 500 cannabis plants were discovered inside a business property. Police forced entry into the building and once inside discovered a large-scale cannabis cultivation spanning several rooms and two floors.