Bob Ostin & Harry Idanov
This is a wonderful trick. It was shown to me by Bob Ostin in the 1970s. Bob was a kind and inventive fellow who became something of a mentor. He had a lot of experience as a professional entertainer, having worked on club, cabaret, and kids' shows earlier in his life but, when I knew him, he was a modest and enthusiastic amateur who always had some magical novelty to show. A simple method and an entertaining premise were hallmarks of his work.
Bob learned The Lie Detector trick from his pal Harry Ivanov. They were both members of the Mahatma Circle of Magicians in Liverpool and, together, they marketed another version of The Lie Detector via Ken Brooke. That version used punched cards. But the version here uses a regular deck and features a bit of business by Bob that really sells the effect.
A card is selected and lost in the deck. The spectator is invited to lie or tell the truth as the performer asks several questions about the identity of the chosen card. Each answer is spelled from the deck, one card at a time. The answers always lead to the selection.