The Francis the talking mule series came to a limp end with both Donald O'Connor and Chill Wills as the voice of the mule no longer in the series. Mickey Rooney somehow got talked into this very silly film and to compensate overacted outrageously as to not have the mule steal any scenes. And stealing scenes from Rooney was not easy.
No longer an army mule Francis is put out to pasture and he meets an old friend in Mickey Rooney. He meets him to tell him a murder has been committed and to leave town yesterday lest he get involved. Of course Rooney the boy scout tells the cops and then spends the rest of the film trying to explain he heard it from a mule. The more he explains the more he's suspected.
In fact several more murders occur and it all centers around a haunted Scottish castle something like the one that Eugene Palette moved to Florida in The Ghost Goes West. All the stuff from Universal's Gothic horror days, sets and props, come into play as Rooney decides to solve the mystery.
It's all real silly, in fact the whole series was kind of silly. Francis In The Haunted House sputters the series to an ignominious conclusion.