The Three Hostages, first published in 1924, is the fourth of John Buchan’s five ‘shockers’ featuring Richard Hannay, and is a personal favourite of mine. The book tends to be overshadowed by the wartime trio of The Thirty-Nine Steps, Greenmantle and Mr Standfast, but this is a shame. Although the hero is joined by some familiar faces, notably his feisty wife Mary, and Scottish laird, adventurer and master of disguise, Sandy Arbuthnot, the book represents a change of pace compared with the previous novels in the series.
Set seven years after The Thirty-Nine Steps, it pits Hannay against a charismatic rising star of the political firmament, Dominick Medina. Medina is a complex character, and perhaps Buchan’s most memorable villain. On the face of it, he has it all: he is a gifted scholar, a first-rate sportsman, and handsome, witty and charming to boot. Everyone agrees, including Hannay to begin with, that here is a man who will go on to do great things. Behind this veneer, however, Medina is ‘utterly and consumedly wicked’, with a burning passion to bend men’s minds to his own will. The three hostages of the title are the victims of an international conspiracy, with Medina at its centre, to hypnotise members of the families of important public figures and then manipulate them for criminal ends.
When Hannay is first asked to help find the hostages, the only clue lies in some cryptic lines of verse which the malefactors have left dangling tantalisingly in front of their pursuers. Hannay is forced to wrestle with obscure classical and literary references in order to track them down, and the recollection of an equally arcane Latin quotation overheard by Sandy finally leads to Medina.
The atmosphere of The Three Hostages may lack the derring-do of some of Hannay’s previous adventures, but the suspense is no less effective. We have the satisfaction of seeing Medina’s intellectual puzzle unravelled, and subsequently Hannay is locked in a desperate battle of wills with this latter-day practitioner of the black arts, as the hero is forced to feign submission in order to gain Medina’s confidence. This part of the story is played out, not against the familiar Buchan backdrops of European capitals, battlefields or the wide-open spaces of the Scottish countryside, but in claustrophobic dimly-lit libraries and sinister doctors’ surgeries. Once Hannay’s cover is blown, however, the action shifts to the outdoors, and the nail-biting dénouement sees the two men meet for a literally cliff-hanging final scene in the Scottish Highlands.
The Three Hostages is a haunting novel, given added poignancy by the subsequent history of the 20th century. Buchan believed that the post-1918 world was morally adrift, that its ‘screws were loosening’ as one of the characters in the book puts it. His experiences in the Great War had taught him, as so many others, that there was but a thin and all too fragile barrier between civilisation and barbarism. His fears would receive grim confirmation in the events of the twenty years following the book’s publication.
Neil Davie,  2001

The Three Hostages (1977, TVM, Clive Donner) https://www.imdb.com/title/tt0076817/ Introduction to the made for TV version in 1977 with Barry Foster as Richard Hannay, Diana Quick, John Castle, Donald