Lois Hargreaves calls on Blunt's detective agency after someone sends her a box of chocolates laced with a mild, though not lethal, amount of arsenic. The Beresford's agree to travel to her home the next day but that morning, read in the newspaper that many members of Miss Hargreaves household were killed the previous afternoon from eating poisoned sandwiches served at tea. There are several suspects, including Lois' best friend from school, a cousin who would inherit a great if she died and several members of the household staff who are acting as if they have something to hide.
—garykmcd