Twin brothers Jack and Seraffimo Spang are controllers of the “Spangled Mob”; a crime syndicate which operates widely in the United States. Together the brothers establish a diamond smuggling 'pipeline' reaching from Africa to North America.
Under the pseudonym "Rufus B. Saye," Jack Spang operates the London branch of the House of Diamonds, a gem importer/exporter purchased by the brothers five years prior to the novel. Casual questioning, however, reveals that "Saye" knows little of the actual stones. Spang also oversees the smuggling operations of the Spangled Mob, giving instructions to smuggler Tiffany Case and the Spangled Mob's chief enforcers, Mr. Wint & Mr. Kidd, under the identity of "A B C."
Serrafimo Spang operates out of Las Vegas, where the Spangled Mob owns the Tiara Hotel and casino. His criminal activities made him extremely wealthy, and he used some of the proceeds to purchase two ghost towns outside of Las Vegas and a locomotive to run between them.
While James Bond is posing as a diamond smuggler in order to infiltrate the Spangled Mob, his cover is blown and he is captured by Serrafimo's men. Spang orders his chief enforcers, Wint and Kidd, to beat Bond to death, but he escapes with the help of Tiffany Case.
Bond chases Serrafimo on the train and he shoots him in the leg before escaping on a mine cart with Tiffany. Serrafimo's train then derails, due to his now shot leg.
After Seraffimo's death, Jack orders Wint and Kidd to kill James Bond and Case on an ocean voyage from the United States to London, and begins to close down the smuggling operation by killing the operators. Jack Spang is killed at the end of the novel when Bond shoots down his helicopter.