For some time now strange things have begun to happen to advertising agent Harry Calvert: first his wife left him for another, then he noticed that he was being followed, he was beaten in a bar, and upon returning to his apartment he discovered that someone had been rummaging through his things. Trying to understand what is happening, Harry finds out that all this is happening because of a receipt for illegally acquired paintings by a Flemish artist that accidentally ended up in his mail. And then Harry faces a problem - give the receipt to the police and punish the criminals or sell it to bandits for good money... The novel was also published under the title “Something Occasionally”