The authors try to trace the history of the famous Koh-i-Noor which is the 89th biggest diamond in the world apparently. The book starts with the Koh-i-Noor being taken from the young ten year old Duleep Singh, son of Maharaja Ranjit Singh handing over the kingdom and the K to the British who promptly send it off to the Queen. Th Sikhs are defeated in the Battle of Chillianwala with the British after the death of the King and that's that. K has always remained with the British since, exhibited with the Peacock Throne of Shahjehan. Other famous diamonds that are compared with the K are Darya i Noor (Teheran), the Great Mughal diamond (Russia).

Historically Golconda mines were the only source of diamonds in the world from the Kollur mines on the banks of River Godavari until the Brazil Mines were discovered in 1725. The Golconda diamonds were extracted from river beds as natural crystals. The diamonds were described as heavenly bodies where Gods dwelled in them and bought prosperity and many wives as well Diamonds are mentioned in the Garuda Purana. Some Hindus believe it is the mystical Syamantaka mani. Anyway there is no right connection - perhaps the Ghoree dynasty acquired it, then the Tughluqs, the Syeds, the Lodhis and then the Mughals until Muhammad Shah Rangila (who definitely had the K with him).
Anyway, they say that Babur got a gift of a diamond which everyone thinks is perhaps the K, but was known as Babur's diamond. His son Humayun almost lost it, and used it to trade off his protection with Persian King Shah from where it somehow made its way to India and the Sultan of Ahmad Nagar Nizam Shah. There's no proof of the diamond being the K though the Mughal treasuries were full of expensive stuff (12 treasuries - 9 for cash, 3 for stones and jewels). Perhaps the first known fact is that a trader Mir Jumla presented a diamond (possibly the K) to Shah Jehan which was is embedded in the peacock throne.
While Muhammad Shah, a peace loving patron of arts was ruling Delhi, Persian warlord Nader Shah seized the Persian throne in 1932 and then invaded Delhi (1739) and defeated a disorganised Mughal army. In teh aftermath, thanks to a rumour that Nader Shah was poisoned and killed the residents of Delhi apparently rebelled and killed some 3000 Persoan soldiers which drew Nader Shah's wrath. the next morning he began a systematic killing of citizens in Delhi and killed 30000. He did not stop until the Nizam of Deccan begged on his knees to stop and promised a purse of 100 crore. Shah looted Delhi in the two months he was there, he took away the K which was studded in the Peacock Throne (which cost thrice as much as the Taj Mahal to make) from Muhammad Shah along with a lot of Shah's wealth (and the Nizam Ul Mull's wealth). They say that Nader Shah found out that the K was taken out of the peacock throne and was in Muhammad Shah's turban and he made a gesture of exchanging turbans and thus got his hand son the K. The loot was taken away on 700 elephants, 4000 camels and 12000 horses.
Nader Shah seems to have handed the K and the Timur Ruby to his chief Afghan body guard Ahmad Khan who seemed to have kept it in his possession for a hundred years (1713-1813). In between the Durrani's (Ahmad Shah Durrani) from Afghanistan raided Delhi and plundered it in 3 raids each more brutal than Nader Shah's raid, defeated the Marathas in Panipat and returned to Afghanistan. Shah's son Timur Shah took over after the death of his father and it was then that the British annexed the Shah Zaman empire. Ranjit Singh was then a feudal who was gaining ground with the British.
Ranjit Singh the had his eyes on the K which was with the descendant of the Afghans Shuja Ul Mulk, who sought protection from Ranjit Singh. In exchange Ranjit Singh got the K which he kept with him on his arm until 1939 when the British took it away from Duleep Singh. The K was with the Sikhs for 36 years.
The K was taken under great security to Bombay for transportation to England - the ship had an outbreak of plague, then it encountered a severe storm and finally made it to the Queen who was rather lukewarm in her reception. Her husband Albert however ensured that the K was given prominence in the Great Exhibition and then, since it did not draw as much attention, got diamond cutters from Netherlands to work on it - they reduced its size by quite a bit in their efforts to make it more luminescent.
Ranjit Singh had 17 wives (many of them committed Sati when he died). Though Ranjit Singh willed that the K be given to the Jagannath temple of Puri after his death, his wish was not followed and it remained with the Sikhs. His descendants (3 Maharajas and 2 crown princes and one dowager queen) died unnatural deaths until the 10 year old Duleep Singh was put on the throne, separated from his mother Jindan who was a wily and able ruler and send her off to a prison in the North.
Duleep was placed in the care of an English couple, the Logins, who brought him up well. Duleep cut his hair, became anglicised, converted into Christianity, became a good friend of Queen Victoria and became as British as any. He met his mother Jindan who escaped from prison and was then incarcerated in Nepal. Jindan got to England and lived with her son until she died. Duleep became and alcoholic, married some random woman, troubled the British for money and his inheritance until he died. Queen Victoria died. Duleep died.
The K remains in the Tower of England along with the Peacock Throne. India, Pakistan, Afghanistan and others claim their ownership of the K which they say is unlucky for men and not so unlucky for women.