Muddle the cucumber and simple syrup. Add Pimms and lemon juice, then shake with ice and strain into a chilled Collins glass filled with ice. Top with 1 oz. Fever Tree Ginger Ale. Garnish with a cucumber wheel.
James Pimm became famous for his "house cup," a gin sling with a proprietary mix of liqueurs and fruit extracts in the 19th century. —Lucius Beebe, The Stork Club Bar Book, 1946