In Holland, poor but industrious and honorable 15-year-old Hans Brinker and his younger sister Gretel yearn to participate in December's great ice skating race on the canal. They have little chance of doing well on their handmade wooden skates, but the prospect of the race and the prize of the silver skates excites them and fires their dreams.
Hans' father, Raff Brinker, is sick and amnesiac, with violent episodes, because of a head injury caused by a fall from a dike, and he cannot work. Mrs. Brinker, Hans, and Gretel must all work to support the family and are looked down upon in the community because of their low income and poor status. Hans has a chance meeting with the famous surgeon Dr. Boekman and begs him to treat their father, but the doctor is expensive and gruff in nature following the loss of his wife and disappearance of his son. Eventually, Dr. Boekman is persuaded to examine the Brinkers' father. He diagnoses pressure on the brain, which can be cured by a risky and expensive operation involving trephining.
Hans offers his own money, saved in the hope of buying steel skates, to the doctor to pay for his father's operation. Touched by this gesture, Dr. Boekman provides the surgery for free, and Hans is able to buy good skates for both himself and Gretel to skate in the race. Gretel wins the girls' race, but Hans lets a friend â who needs it more â win the precious prize, the Silver Skates, in the boys' race.
Mr. Brinker's operation is successful, and he is restored to health and memory. Dr. Boekman is also changed, losing his gruff ways, thanks in part to being able to be reunited with his lost son through the unlikely aid of Mr. Brinker. The Brinkers' fortunes are changed further by the almost miraculous recovery of Mr. Brinker's savings, thought lost or stolen ten years ago.
The Brinker parents live a long and happy life. Dr. Boekman helps Hans go to medical school, and Hans becomes a successful doctor. Gretel also grows up to enjoy a happy adult life.

Question: Why is Dr. Boekman gruff in nature?
Answer: The doctor is gruff because his wife dies and his son disappeared.
Alternative answer: he has lost his wife and his son has disappeared