What are the motifs in The Thirty-Nine Steps by John Buchan?

The classic British spy is a recurring idea in the story. Hannay bears the classically British "stiff upper lip," a stoicism or certain detachment that allows him to make light of even the most dire situation. When Hannay discovers Scudder dead, Hannay takes up Scudder's mission because "I hate to see a good man downed"; when Hannay is caught in the lie of being a Free Trader, he rises to the occasion and delivers a rousing speech as if he were a Free Trader, though he has no idea what that means. When confronted with his identity exposed by the old German spy, Hannay doesn't break down but instead creates, on the spot, a sophisticated alias to thwart and confuse his enemy.