 Although the books started in the late 1980s and have continued into the millennium, Nick and Tim remain roughly the same age (14 and 28 respectively), while London changes with the times (the newer books feature Oyster Cards and computers for example, whereas the older books feature parts of London that have long since changed, such as smoking in offices).The entire series was re-issued in 2007 with new covers.When released in the North American market, although the stories remained the same, the currency was changed