Young family of Volkov's, Oleg and Katya, move to an apartment they bought and get acquainted with their neighbor, locksmith Arnold Sharapov.

Frustrated Oleg decides to drown his sorrows in alcohol, but at the bar accidentally meets Ivan Petrovich Prokhorov, pensioner, whose wife in his time was also unfaithful.

After some hesitation Oleg decides to do the terrible thing, but random interference from his mother-in-law Eugenia Ivanovna Kholodkova saves the wife of the hapless poisoner.

On the advice of the insidious mother-in-law Evgenia Ivanovna, Arnold and Katya want to invite Oleg and Zoya to dinner together and poison them by feeding them contaminated burgers.

Learning this, Oleg first seeks the advice of experienced poisoner Prokhorov, who offers a number of retaliatory steps brilliant in their deviousness.