The Seven Dials Mystery by Agatha Christie

When a practical joke at a country house party turns deadly, amateur sleuth Lady "Bundle" Brent finds herself drawn into a web of international intrigue. Following a trail of cryptic clues centered around London's Seven Dials district, Bundle uncovers a sinister conspiracy threatening national security. With help from charming secret agent Jimmy Thesiger, she must unmask a murderer and expose a criminal organization before more lives are lost in this gripping mystery from the Queen of Crime.