Build a suspenseful scene by using time constraints. Write a scene where time is on the side of the antagonist. Turn the heat up on the protagonist by throwing obstacles in the way every time he seems to be making progress. Make each situation believable.
Invent a crisis for the protagonist to get the reader to empathize with him. Make the crisis one that is so serious that he will do anything to prevent it from happening. For example, a child is trapped in a burning house and the mother has broken her leg escaping and cannot go back inside to rescue him. Add as many devastating circumstances as possible to build the suspense.
Present one challenge after another that requires hard choices or decisions. Test the character's stamina. Make it a losing situation for the protagonist. Give the scene a moral conflict, such as tempting the moral protagonist with immoral actions that test his strength of character and resolve. Be relentless in presenting one temptation after another.
Stretch the skills and strengths of the protagonist as far as possible. She must work against enormous odds. The antagonist must apply lots of pressure to the protagonist unrelentingly, but she should never give in or break. For example, the protagonist is the adopted mother of a child whose birth mother wants her back. She has exhausted all legal processes and is faced with giving the child back.