At the beginning of the novel, Robert Jordan prides himself on getting the job done without thinking. He has no time for women in his life, and values being cold and fearless unlike the last man, Kashkin, who was sent to blow up a bridge with Pablo. However he doesn't count on meeting Maria, who immediately makes him feel things he hasn't felt before, and it confuses him. When she responds to his touch, and later comes to him under his sleeping robe, he knows he is in love with her. But even being in love doesn't stop him from doing his duty.
Maria, who has been traumatized by her treatment at the hands of Nationalist soldiers, acts as a dutiful daughter to Pilar. But when she meets Robert Jordan, she recognizes something in him that makes her fall in love with him. With Jordan, Maria is not only able to feel real love and pleasure with him as they make love, but she also wants to become his wife. They "marry" under his sleeping robe, and dream of truly marrying in Madrid, though Jordan believes they will probably die in the bridge explosion mission.
Pilar is the real leader of Pablo's guerrillas because Pablo, a heavy drinker, has lost his ability to set aside his fear. He doesn't want to die, and he lets that get in the way, but he tells Pilar about it and hands over the leadership to her. Pilar takes care of all of the guerrillas, making food and good decisions. She also serves as Maria's guardian, making sure that Maria and Robert Jordan have time together once she realizes they are truly in love.
Pablo begins the novel by refusing to blow up the bridge or help with the mission in any way because it would alert the Fascists to his band's position in the mountains, and he wants to keep them safe. Anselmo shames him into agreeing to take Robert Jordan in, and later, Pilar shames the drunken Pablo into agreeing to help. Pablo ruins the original explosion plan by stealing the detonator and fuses and tossing them in the river, but he tries to make up for it by gathering help and horses, in order not to have to live without Pilar, despite her tendency to berate him for his drinking.
Anselmo begins the novel asleep, and sleeps on the ride to the mountains, but he is an excellent guide for Robert Jordan. He remains with Jordan throughout his exploration of the bridge and helps to blow it up, but loses his life in the process.