Tamaya loves to draw castles and knights. But one day, she feels too tired to do so. At the hospital, Tamaya learns she has leukemia. Her doctor explains that her white blood cells are like knights who protect her body from bad germs, but hers are sick and need to be replaced. And so, her courageous journey with an allogeneic hematopoietic stem cell transplant begins. Within the "castle" of her hospital room, Tamaya is surrounded by her devoted medical team, loving family, and loyal toy elephant, Gugu. Though some battles feel hard, Tamaya imagines her new stem cells as brave little knights-marching forth, training, and growing stronger each day to protect her once more.