Inspector Maigret requests permission to let a prisoner from a maximum security prison “escape”. He was convicted of having killed a rich American, Mrs. Henderson and her French maid, Elise Chatrier, at saint Claud. But Maigret is convinced that this man, Joseph Heurtin, was either innocent or mad, even if his fingerprints and footprints were found everywhere, he was seen in the neighborhood and he dropped a Paris-Saint Calud ticket. What puzzles maigret is that he seemed to have absolutely no reason, nothing was stolen from the house but the convicted refused to say anything in his favour. The accused does not seem surprised to find the note for the escape plan, this is why Maigret thinks that there is someone else involved. The day after his escape, he finds a note telling him that this was just a police setup, a note received from someone who knew something. The paper of the note was from the American bar Coupole, where Maigret goes and sees Johann Radek, a Czech medical student. Heurtin, who had managed to elude his police followers, seems to be waiting outside for Radek, who has himself arrested for failing to pay his bill.
Radek gives Maigret banknotes which can easily be traced to William Kirby, Henderson's nephew, who had also been in the Coupole. Maigret goes back to Saint-Cloud, and finds William-Kirby in the house, but by the time he reaches him he's killed himself, shot in the head. Radek taunts Maigret, who continues to silently follow him everywhere. Finally they return to the Citanguette, where Heurtin had first slept on escaping from the Santé, and they see Mrs. Kirby go to his room and tear up a mattress. They then follow her taxi to Saint-Cloud, where she goes into the house, returning in half an hour with a small package. But Maigret refuses to follow her and brings Radek into the house, where he reveals Edna Reichberg, Kirby's mistress and his wife's friend, in a closet. Radek realizes he's caught, and shoots at Maigret, but the inspector has had the bullets removed.
Even if Maigret had known all along that Radek was the brain behind all these murders, he still has a hard time proving his gilt, because, apparently, there is nothing to connect him with the crimes.
The review of this Book prepared by Dana Samson