The plant is in a seemingly impregnable location beneath an overhanging cliff at the end of a long, narrow fjord lined with numerous anti-aircraft guns. The only way to destroy the plant is by bombing the cliff until it collapses and buries the facility, a job for 633 Squadron's fast and manoeuverable de Havilland Mosquitos. The squadron trains in Scotland, where there are narrow glens similar to the fjord. There, Grant is introduced to Bergman's sister, Hilde. They are attracted to each other, despite Grant's aversion to wartime relationships.