The fifth season opens with the Wall Street Crash of 1929, and the Shelbys have lost a great deal of their income as their ill-gotten wealth was heavily invested in the American stock market. This forces Tommy and Arthur (Paul Anderson), now the chairman of Shelby Co. Ltd. in Tommy's absence, to rely more heavily on the family's more familiar criminal enterprises, including making cash deals with high court judges to take out vile men or striking deals with the Chinese to transport pure-grade opium. It also opens the door for what is, unfortunately, a very timely story about the rise of fascism in the years leading up to World War II.
But financial woes and fascists are the least of Tommy's worries this season, as much of his turmoil once again stems from his internal scars. Tormented by suicidal thoughts brought on by his own swirling, guilty conscience, Tommy's death wish makes him increasingly unstable. Relying on laudanum to dull his lingering grief and the pain his rise to the top has ultimately caused him and those he loves, he's not sleeping, hallucinating apparitions of his murdered wife Grace (Annabelle Wallis), who appears to him and accuses him of not only killing her but also attempts to persuade Tommy to join her in death.
Contributing to Tommy's uneasy mental state this season is the fact he has also become convinced that someone close to him is after his crown, namely his cousin Michael (Finn Cole), who ignored Tommy's order to sell their stock before the crash. It's difficult for Tommy to accept that Michael's ideas for the company might actually be a path toward greater success in the future — and might relieve some of the pressure from his own shoulders — so he and Arthur continue to cling to the way things have always been done.
But Michael isn't the only person who wants something from Tommy. The Billy Boys from Scotland want his racetracks in the north, while Sir Oswald Mosley (Sam Claflin), a fictional version of the very real, very controversial Member of Parliament who founded the British Union of Fascists in the 1930s, wants to use his popular support to help launch a new party. Tommy wants to bring him down because he believes it's the right thing to do, but a number of roadblocks are also created by his own hand in attempting to do so.