In C.S. Lewis' The Horse and His Boy, Narnians King Edmund and Queen Susan have gone to Tashbaan so that Susan can determine if she wishes to marry Prince Rabadash of Tashbaan. However, she has quickly realized that she does not, and here is the trouble. Let's look at this in more detail.
Susan has now seen the prince for who he really is. When he visited in Narnia, he put on a splendid show with his "marvellous feats" in the tournament and his courteous behavior. At home in Tashbaan, though, the prince exhibits another character entirely. In fact, as Edmund says, he is "a most proud, bloody, luxurious, cruel and self-pleasing tyrant." Susan wants nothing more to do with him.
Yet getting out of Tashbaan may not be so easy for the Narnians. Edmund recognizes their danger. The prince does not like being denied, and he could become a dangerous enemy. What is more, the Tisroc, ruler of Calormen, has long desired Narnia for his own. Holding Edmund and Susan as hostages might be just the trick to gain some leverage for himself. Edmund is afraid, too, that Susan's rejection of the prince might start a war with themselves caught in enemy territory or even that the prince might try to take Susan by force. There are many possibilities, none of them pleasant.