Jack London used to buy story ideas from the young Sinclair Lewis. He blamed his “damnable lack of origination”: “I’m damned if my stories just come to me,” he wrote. “I had to work like the devil for the themes.”

Of the 55 plots that Lewis sent him, London bought 27, paying $137.50. Of these, London used five: three for published short stories (“When the World Was Young,” “Winged Blackmail,” and “The Prodigal Father”), one for a novelette (The Abysmal Brute), and one for a novel that he never finished (The Assassination Bureau).

He once wrote to Elwyn Hoffman, “expression, you see — with me — is far easier than invention.”