A tourist found himself locked inside a Waterstones book shop for two hours after it closed while he was still browsing, BBC reported.
David Willis, from Texas in the United States, got trapped in the branch in Trafalgar Square, central London, on Thursday night.
When he was finally released, he tweeted: "I'm free."
He said he had been upstairs in the shop for 15 minutes and when he came down all the lights were out and the doors locked.
'Please let me out'
Mr Willis posted a picture of himself on Instagram behind shutters with the message: "This is me locked inside a Waterstones bookstore in London."
In a later post, which by Friday morning had been retweeted by more than 8,000 people, he tweeted: "Hi Waterstones, I've been locked inside of your Trafalgar Square bookstore for two hours now. Please let me out."
A Metropolitan Police spokesman said police were called at about 21:35 BST "by a man claiming to be locked inside a shop".
He added: "Officers attended and following the arrival of a key holder the man left the building shortly after 11pm."