The British secret service agent Michael Reynolds was in trouble only hours after he entered Hungary, only a few years after the Hungarian Revolution.  He falls into the hands of the Hungarian state police, but by pure luck the colonel that intercepted him is a double agent, so after a frightening few hours he ends up with the organisation he was supposed to get in touch with.  This organisation is going to help him get in touch with professor Jennings, a man who was lured behind the Iron Curtain, and whose expertise in the math used in ballistics will prove to be vital to the West.

So a first contact with the professor is attempted in a hotel where the scientist is preparing for a conference.  The contact is made, but the Hungarion secret police finds out about the plot.  From then on a chessgame starts, with moves and countermoves by both sides, with a strategy that depends on a lot of unknown factors, and with a very uncertain outcome...

MacLean uses a tried recipe.  Chances are slim to start with, and it gets worse from the start.  The exhausted hero seems to get setback after setback, but stubbornly continues until he reaches his goal.  And don't forget the touch of romance latently present.  The proven recipe works, from page one the tension builds and it isn't until the last page you're really sure everything is over, and in between you keep turning pages to find out how the current developments develop, or how the next setback will be overwon, if it will be.

MacLean also uses something less familiar.  Jansci, the leader of the group Reynolds makes contact with, is a mild pacifist, surprisingly mild towards his enemies particularly once you learned his past.  MacLean gives Jansci a lot of time to explain the reasons for his pacifism, and a lot of time to try to convince the tough British agent that his pacifism is the only way to get out of the cold war that is dominating the world at that time.

I don't think the pacifistic speeches ought to have been omitted at all, but reducing the page-long monologues could have made the story stronger.  Now it's just an average MacLean, which is, don't get me wrong, still an impressive adventure story.  A bit outdated here and there - it's hard to imagine a "modern" secret service without decent communication equipment, but since the era is from so long ago it's easy to forget this story plays around 1958 - and a bit too much preaching here and there, but still a strong pageturner.