When Lions Roar begins in the mid-1930s at Chartwell, Winston Churchill's country estate, with new revelations surrounding a secret business deal orchestrated by Joseph P. Kennedy, the soon-to-be American ambassador to Great Britain and the father of future American president John F. Kennedy. From London to America, these two powerful families shared an ever-widening circle of friends, lovers, and political associates ??? soon shattered by World War II, spying, sexual infidelity, and the tragic deaths of JFK's sister Kathleen and his older brother Joe Jr. By the 1960s and JFK's presidency, the Churchills and the Kennedys had overcome their bitter differences and helped to define the ???greatness??? in each other.