agony column:

Holmes often turns to the agony column — ENGR: “Sherlock Holmes was, as I expected, lounging about his sitting-room in his dressing-gown, reading the agony column of The Times and smoking his before-breakfast pipe” — for clues or to lay a trap for a suspect or gather information. The agony column was the classified advertisement section of a newspaper where family members appealed for a wayward child to come home or the destitute appealed for money or criminals maintained private communications through cryptic messages.