"in the fourpenny boxes in the Charing Cross Road"

The Charing Cross Road is a street in London where numerous bookshops, selling both new and second-hand books, may be found.

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One of the bookshops on this road, Marks & Co., was partly the setting for the 1987 film 84 Charing Cross Road which was based on Helene Hanff's true story of the same name.

         

 

1937 penny
Public Domain1937 penny - Credit: Welkinridge, Wikimedia Commons
1943 threepenny bit
Public Domain1943 threepenny bit - Credit: Welkinridge, Wikimedia Commons

The 'fourpenny boxes' would have been those containing the cheapest books. Fourpence in pre-decimal coinage would be approximately 1.66 new pence in present-day coinage. 

In the old coinage, fourpence could be made up of 4 separate pennies, 8 halfpennies, or a penny and a threepenny bit.