Motive v. Oportunity

At one of the Tuesday Club meetings, Petherick presents his case. The beloved granddaughter of old Simon Clode dies from severe pneumonia. Desperate, Clode hires Eurydice Spragg, a medium. He is so grateful for the medium's work that he decides to sign a will in her favor, but something strange happens with the document. Will Miss Marple solve this mystery?