Out of all the characters in the novel, Etienne arguably undergoes one of the biggest transformations in terms of his behavior and perspective. Marie-Laure’s arrival at his doorstep acts as a shock to his quiet, reserved life, and overtime, the two of them help each other to realize their full potential. Marie-Laure’s father first mentions his uncle to her as they are fleeing Paris, suggesting that he is “partially crazy” due to his experiences during the first World War. Although they do not have the language to describe Etienne’s condition in the 1940s, the visions he sees and his fears of leaving home imply that he suffers from post-traumatic stress disorder, or PTSD. The psychological challenges that he faces make it virtually impossible for him to go outside and inevitably cut him off from the rest of the world, leaving him to suffer alone. Although Madame Manec does everything she can to assuage his fears, Etienne meets his true match when his grand-niece comes to live with him in Saint Malo. They have similar interests, such as a passion for science and love of reading, and they both know what it feels like to lose contact with the world. Etienne and Marie-Laure may have different disabilities, but they know isolation in a way that none of their loved ones do.

Marie-Laure’s presence at Number 4 rue Vauborel begins pulling Etienne out of his reclusive ways, although the major shift in his character does not occur until late in the novel. Having a youthful energy in the house slowly lifts his spirits, and he bonds with his grand-niece through playing games, reading stories, and sharing his love of radios. The close relationship that Etienne and Marie-Laure develop as the war drags on gives a new sense of purpose to his life, although at the same time, he desperately fears losing it. While he may attempt to shield her from danger by forbidding her to participate in the resistance with Madame Manec, the unwavering resilience that she shows in the face of adversity allows him to believe that he, too, possesses an internal strength. The example that Marie-Laure sets gives him the courage to continue the resistance work that Madame Manec began, a role which marks a significant departure from the shut-away life he led prior to the war. Etienne’s transformation does not reach its true peak, however, until he rushes out of the house to find Marie-Laure after she fails to promptly return home. This moment highlights the depth of the love he has for her and signifies his new relationship to the world around him.

For as much as Marie-Laure helps Etienne overcome his fears, he also helps her grow and teaches her skills that prove paramount to her survival. He does his best to help her feel comfortable when she first arrives in Saint Malo, and as their relationship develops, he does everything he can in order to keep her out of harm’s way. Doing so allows Marie-Laure to flourish in her new environment despite the challenges she faces. Even more importantly, the lessons she learned during their work on the resistance broadcasts allow her to use the radio to save herself from Von Rumpel, and after the war, Etienne helps her lead the life she always dreamed of. His compassion and devotion to family make all the difference for Marie-Laure.