During a dull country house weekend Cornelius Appin, a guest about whom the others know little, reveals that he has spent years researching whether animals can learn to talk and that he has achieved great success with his hosts’ cat Tobermory. When the sceptical house guests investigate, they find that not only is Tobermory capable of conducting a conversation but also that he is worrying indiscreet about private matters he has seen or overheard. In panic, they decide Tobermory will have to be done away with before he can reveal more of their secrets. Appin protests against this attitude towards his scientific breakthrough but is overruled. Poison is prepared but Tobermory does not appear that night for his dinner. The next morning his body is brought in: he has apparently been killed fighting a neighbour’s cat. An epilogue notes the death a few weeks later of a man called Cornelius, killed in Dresden zoo by an elephant.