"Tosheroon" is an odd but memorable name. It sounds amusing and somewhat incantatory - especially for a card trick. Bob Driebeck, who dubbed it, knew that the word was Cockney slang for a half-crown, which is also the type of coin he used to perform this offbeat card trick.
The basic effect is a transformation done with an impediment in place - the impediment or obstruction in this case is a coin, which is placed onto the face of the card that eventually changes.
Effect: A card is selected and lost in the deck. Then a borrowed coin is marked and placed onto the face of a tabled deck. The card showing at the face is not the selection. The face-up deck is then given a straight cut to wedge the coin and non-selection in the center of the deck. This placement provides further impediment, making secret manipulations to exchange the non-selection into the selection problematical. How, for example, can the selection be maneuvered under the coin wedged in the middle of the deck? Also, how is it possible to steal or remove cards from under the coin? When the deck is eventually cut again to reveal the marked coin, the coin now rests on the face of selected card!