nine o’clock
Now we are faced with a new problem . We know the cocoa contained no strychnine . The coffee was never drunk . Yet the strychnine must have been administered between seven and nine o'clock that evening . What third medium was there -- a medium so suitable for disguising the taste of strychnine that it is extraordinary no one has thought of it ? '' Poirot looked round the room , and then answered himself impressively . `` Her medicine ! ''