On 2 May 1718, the gunpowder store on the third and fourth floors of the tower ignited. A contemporary record by the Kirk's Session Clerk describes the explosion as having "…Rent the Western Gevell of the Church, broke all the glass windows, and turned the Sclates of the Church, and broke a great deal of the Leadden high roof of the Church". The town council's first step was to enclose the eastern four bays with a wall in which stood a turnpike stair. Galleries were then added to make up for lost space; the former north door was moved one bay east and its keystone was adorned with a carving of an angel's head; plaster ceilings, coombed in the aisles and barrel-vaulted over the nave, were raised. In November 1719, the town council commissioned Alexander McGill to build a new church in the western half with Gilbert Smith as mason. McGill's plans effectively reversed the design of the existing church. The remains of the tower were demolished and two new bays were added to the west end of the damaged bays. This created spaces for two congregations: Old Greyfriars at the East and New Greyfriars at the West. Inside New Greyfriars, galleries on the north, south, and west sides faced a pulpit against the middle south pillar.