To call Thae Yong-Ho’s career trajectory remarkable is an understatement. Following a stellar career as a North Korean diplomat, culminating in his appointment as deputy ambassador in London, at age 54 Thae and his family defected to South Korea. However, once in Seoul he quickly tired of his sinecure at a think tank, entered politics and within four years of defecting was elected to South Korea’s national assembly. And in his free time, he wrote a book.

Thae is one of the highest-ranking officials ever to defect from North Korea and his book, Passcode to the third floor: An insider’s account of life among North Korea’s political elite, is the most detailed insider account so far written about the country’s political system. Thae not only describes the dramatic personal events leading up to his defection; he also provides a tell-all account of how North Korea’s government works, including its top leadership, foreign ministry and security apparatus.

Thae entered government service in 1988 and his book spans nearly three decades of foreign and security policy, from the country’s nuclearisation to the power transition from Kim Jong-Il to Kim Jong-Un. Like most North Korean diplomats, he studied at Beijing’s Foreign Languages University and the Pyongyang University of Foreign Studies. Classes in negotiation skills were particularly rigorous and taught trainees how to prepare physically and mentally, as well as a range of tactics from occupying the high ground to breaking negotiations.

Thae sees Kim Jong-Il’s gradual rise to power in the 1970s as the turning point that made North Korea’s authoritarianism absolute. Kim shifted decision making from the cabinet to the Workers’ Party of Korea and, ultimately, to himself. He introduced a highly centralised system of administrative control, with written proposals sent up to his secretariat on the third floor of the party’s central office, and orders handed down. Even trivial matters were decided at the top, while ministries were kept isolated from each other. Kim Jong-Un has kept the system unchanged.

North Korea’s top bureaucrats lead a well-rewarded but precarious existence, at constant risk of being called to the third floor. Praise is rare, while minor slip-ups may require a self-criticism session. Major errors can lead to banishment from Pyongyang or a spell in one of North Korea’s notorious prisons. Thae describes one harrowing instance when Kim Jong-Un was displeased with an official and ordered his immediate execution.

He also recounts how intimidation and the siloed structure of North Korea’s bureaucracy affect the management of its diplomatic relations.

In 2014, North Korea’s national defence commission learned that Britain’s Channel 4 was producing a fictional TV series about a British scientist being detained and forced to help North Korea to develop nuclear weapons. Without consulting the foreign ministry, the defence commission wrote directly to the British foreign office demanding that Channel 4 halt production and threatening an ‘unimaginable act of retribution’. The British government was shocked, and the embassy in London was left to convince its counterparts that North Korea had no plans for a terrorist strike.

When a nearby London hairdressing salon put up a picture of Kim Jong-un with a caption referring to his ‘bad hair day’, the diplomats’ careers were on the line. Thae and a colleague quickly visited the salon and demanded that the owner take the picture down. ‘When we speak nicely, it’s best to listen’, they threatened. The British tabloids had a field day with the incident.

North Korea watchers fall in two broad groups: pessimists who see little prospect for change and optimists who, despite the recent hardening of North Korea’s policies, see scope for an eventual opening and even some form of denuclearisation. Thae falls firmly in the former category.

Thae’s pessimism derives from what he sees as Kim Jong-Un’s deep-seated insecurities. Kim’s mother was never formally recognised as Kim Jong-Il’s wife, and there are no photographs of him with his grandfather Kim Il-Sung. As a result, Kim is insecure about his all-important bloodline and feels he has to use strong-arm tactics to bolster his position, not least by continuing to develop North Korea’s nuclear arsenal. Thae doesn’t think this will change.

Given the abundance of personalities in Thae’s account and the similarity of many Korean names, the book would have benefitted from a list of key players, a family tree of the Kim dynasty and an index. But compared with the treasure trove of information that Thae offers, these are minor shortcomings.

Passcode to the third floor is a fascinating read for both specialists and generalists.