What happens in a Tube station when all the passengers have gone home? Why do Tube workers carry cards about rat piss? And why isn't standing on the right of an escalator necessarily a good thing? Londonist finds answers on our latest nocturnal investigation. Some of London's busiest Tube stations are in a mess. Missing tiles and chicken-wire cornices are a familiar site, especially at King's Cross and Leicester Square. It's a case of......