The story is that a woman and her fiancé, whose code names are Cat’s Pajamas and Pigeon Wing respectively, are planning to murder CP’s cousin, Reggie(short for Regina), in order that CP would inherit the family’s vast pig farm.
To do so they train one of Reggie’s show pigs, who are allowed to wander the gardens unhindered, to charge on command. Reggie is renowned to very dangerously point her letter opener towards herself when opening her mail. So all they have to do is replace her regular letter opener with a specially sharpened one, position the pig in front of the French windows, wait until Reggie is in the process of opening the aforementioned letters, then give the pig its command, thus causing Reggie to accidently stab herself during the collision with said pig. As she has no will nor any siblings, CP will became fabulously rich and be free to marry PW, whose status as a lowly gardener had previously stopped such a union.
But wait, what’s this? Poirot is staying at Reggies manor house the very same weekend the murder is scheduled to take place! What will happen now?