A next of kin is a person's nearest "living blood relative" (Investopedia, "Next of Kin"). Inheritances are often left to the next of kin, and when a deceased person has not written a will, the inheritance automatically falls to the next of kin. In Sir Arthur Conan Doyle's famous detective novel titled The Hound of the Baskervilles, featuring Sherlock Holmes, Sir Charles Baskerville has just died under suspicious circumstances, leaving his inheritance to his next of kin Sir Henry Baskerville, his nephew.
The Baskervilles are a family of barons who live in Baskerville Hall of Devonshire. Dr. Mortenson was a friend of the late Sir Charles Baskerville, who, before his death, gave Mortenson a letter written in 1742 detailing a curse placed on the first Baskerville, Hugo Baskerville. Hugo Baskerville was described as being "a most wild, profane, and godless man" and believed to have been turned into a giant, black hound (Ch. 2). Since that time, it is believed that Baskerville men are supernaturally killed by the same giant hound. Sir Charles has just been found dead with giant hound footprints near him. Due to his death, Baskerville Hall is bequeathed to his nephew Sir Henry Baskerville. Sir Charles left small sums of money to Mr. and Mrs. Barrymore, his domestic servants, and to his friend Mortimer, but the remainder of his money goes to Sir Henry, which is £750,000.
Interestingly, Sir Henry goes to Holmes with a mystery of his own. He has received a letter anonymously delivered to his room in the Northumberland Hotel, warning him, "As you value your life or your reason keep away from the moor" (Ch. 4). The delivery itself was even more mysterious considering that no one knew Sir Henry was staying at that hotel, and it's delivery suggests that someone has been spying on him. As Holmes investigates the mystery, a secret Baskerville relation is uncovered, who has motive to want Sir Henry dead.