The members of the Tuesday Club debate possible solutions between them but Miss Marple hits on the correct one: although she does not know what caused Sir Richard to stumble – possibly a trip over a tree root – it was his cousin Elliot who quickly stabbed him in the pretence of examining him. The knife was hidden as part of his fancy dress costume.
The members of the Tuesday Club discussed potential solutions, and Miss Marple identified the correct solution: although she didn't know why Sir Richard stumbled (possibly a trip over a tree root), it was his cousin Elliot who swiftly stabbed him while pretending to examine him. The knife was concealed within his costume.