Thinking Dr Galipeau is right, despite the fact that the doctor is always wrong whenever he says something (a running gag throughout the movie), Emile, under the advice of the notary dealing with the life annuity contract, accepts to index the 'viager' each year following the course of aluminium - a popular investment in the 1930s.
In 1940, the early years of WWII, an attempt to make Martinet pass for a German spy is foiled by bad timing, as it happens on the day of France's surrender.
This proves fruitless as the boy is perfectly healthy and more than happy to climb steps (he even counts them for his personal enjoyment), smoke, eat and drink like there is no tomorrow.
He invites him for a trip on a paddle boat out to sea where he schemes to shoot him and ditch his body in the water, planning to tell everyone Martinet fell and drowned as a cover-up story.
Hoping to finally see him die, the remaining Galipeau plotters, Léon and Elvire, visit him in the hospital where they find him healed and enjoying life.
Under the disguise of cleaning his house before his return from hospital, Léon and Elvire sabotage the place to have Martinet fall down the stairs of the balcony to his death.
Finally, the last remaining member of the Galipeau family, Noël enrolls two criminal friends as hitmen to kill Martinet while he stages a fireworks show for the old man's 100th birthday as a distraction.