"Fearful" is not a word one would use to describe Mary, the pampered young orphan from India who arrives at her uncle's home in England. The fact that early on in this classic novel, she is given the nickname "Mistress Mary Quite Contrary" tells the reader that she is full of sass and obstinance but not fear.
We are introduced to the character who embodies fear much later in the novel. On a number of occasions, Mary has heard the terrible sound of a child crying in another part of the house but has been unable to glean any information about this child. Eventually, she follows the sound and discovers Mr. Craven's son, Colin, who is ill, neglected, and terrified of everything. His biggest fear is that he will grow up to be a hunchback like his father.
The local doctor who has been treating Colin stands to inherit the property if Colin dies, so naturally he has been feeding the boy all sorts of nonsense about how he is on death's door, so essentially, poor Colin has been locked up with only his own fears and neuroses for company.
Over time, the secret garden and the amazing power of friendship, along with Mary and Dickon, help to allay Colin's many fears.