One of the most secretive organisations in the UK, the surveillance agency GCHQ, sent out a tantalising tweet on Thursday. It took the form of a colourful puzzle made up of emojis.



It was a tease for an announcement on Friday of a new GCHQ puzzle book. The first one in 2016 proved a surprise hit, selling more than 300,000 copies.



The GCHQ Puzzle Book II, to be published by Penguin on 18 October, is billed as a chance to “pit your wits against 100 years of codebreaking genius”.



As well as being published in time to catch the Christmas market, the book will be part of a series of events to mark the founding of the organisation in 1919. The book, will include a series of puzzles related to GCHQ’s history. Alongside anecdotes from staff, there will be a chance to attempt questions set in past entrance exams.



Puzzle Book II will be published by Penguin on 18 October. Photograph: Penguin Books

A Penguin Random House spokeswoman said: “[The book] adds some historical stories from the organisation’s archives which will give readers a snapshot into the challenges that have faced problem solvers at GCHQ for the past 100 years.”

As with the first book, the proceeds will go to charity.

A GCHQ spokesperson said: “We were delighted with the success of our first puzzle book, which raised over £330,000 for the Heads Together campaign, an important cause to change the conversation around mental health.”



The Guardian’s review of the first one described it as “fiendish ... as frustrating, divisive and annoying as it is deeply fulfilling”. Some readers found it too fiendish, complaining the puzzles were too difficult.

Although the follow-up book will still have some tough puzzles, the writers will acknowledge the complaints by including more of the easier ones.

GCHQ until recently guarded its secrecy even more than the other main UK intelligence agencies. It was called the Government Code and Cypher School (GC&CS) in 1919 but, to help disguise its purpose, the name was changed to Government Communications Headquarters.

During the second world war, its staff at Bletchley Park helped break Germany’s Enigma code.



The existence of the organisation was publicly revealed by the journalists Duncan Campbell and Mark Hosenball in a celebrated case in the 1970s. It surfaced again in a spy trial in the 1980s but its existence was only formally acknowledged in the early 1990s.



GCHQ found itself at the centre of unwelcome headlines in 2013 when thousands of top-secret documents that revealed the scale of its surveillance activities were disclosed by the National Security Agency whistleblower Edward Snowden.

Part of the attraction of the first puzzle book lay in its novelty in being written by an organisation of codebreakers and hackers. Follow-up books tend not to do as well as the original, though publicity over GCHQ’s centenary may help sales.

Dan Bunyard, a non-fiction publisher at Michael Joseph, part of Penguin Random House, said: “The 2016 book was the Christmas stocking filler of choice and we’re hoping that this new batch will be as fun, mind-bending and rewarding as before.”