The Door in the Wall written by Marguerite de Angeli in 1949 is a young adult historical fiction novel that takes place in medieval England roughly in the late 1200's through the mid 1300's. The time line is not exact, but historical periods, such as the Scottish Wars, the Black Plague, and the reigns of King Edward I and King Edward II, define the world in which the young protagonist, Robin, lives.
Robin is an unlikely hero even though he is a young noble who is supposed to be trained as a knight. He develops an illness, perhaps the plague itself, as so many around him contract and succumb to the "black death" including his caretakers. Robin's legs eventually become limp and seemingly useless.
A devout friar rescues the abandoned Robin and through thoughtful means helps Robin recover substantially. Robin regains his strength and zest for life even though he continues to need crutches.
After an adventurous and eventful journey to an uncle's castle, Robin finds himself saving the day despite thick fog and dangerous enemies.
To enhance your middle school scholar's understanding of Engand during the early Middle Ages, I would highly recommend this Newberry award-winning book. For an adult interested in historical fiction that takes place during the same time period, I would recommend reading The Traitor's Wife written by Susan Higginbotham, a novel that disgusts and delights its readers at a whirlwind pace.