Later, Mary shows the note to Martha. Martha explains that the nest is a missel thrush nest, and Mary understands that he's promising to keep her secret. Late that night, Mary wakes up to the sound of a storm. She feels as though she hates the rain and thinks it sounds like a person crying. After about an hour of listening, she hears what she believes is actual crying. She slips out of her room and follows the sound. It gets louder as Mary gets to the corridor with the tapestry covering a doorway. Mary pushes open the next door and finds herself in a richly furnished bedroom. There's a crying boy in the bed, and Mary wonders if she's in a dream.
By going out independently, Mary shows that she thinks little of Mrs. Medlock's attempts at guardianship and instead, understands that she needs to figure things out for herself. When this independence leads her to discover the actual cause of the crying sounds—a boy about her age—it suggests that only when a child starts to develop some degree of independence can they take routes that can begin to lead them to other people.
The boy looks ill, but as though he's crying because he's upset and not because he's in pain. When he notices her, he asks if she's a ghost and introduces himself as Colin Craven. The children realize that they're related; Mr. Craven is Colin's father. Colin asks Mary to come closer so he can confirm that she's not a ghost, and he grabs onto her robe. They discuss that neither of them knew the other existed, and Colin admits that he wants to be a secret because he's ill and he doesn't want anyone to see him. He explains that the servants are forbidden to talk about him, and he's going to either die or become a hunchback.
When Colin admits that he wants to be a secret, it shows that children can keep secrets with negative consequences just as easily as adults can. Further, the fact that Colin can forbid the servants to speak about him indicates that, like Mary was in India, he's very spoiled and can shape the world within the manor to suit his whims and desires. This suggests that going forward, this will be one of things that he reevaluates, like Mary is doing.
Mary remarks that everything in this house is a secret and asks if Mr. Craven comes to see him. Angrily, Colin says that his father hates him because Mrs. Craven died. Mary says that he hates the garden for the same reason, but she doesn't tell Colin what the garden actually is. Colin goes on to say that he's been here most of his life. He wore a brace for a while, but then a London doctor said the brace was useless and prescribed fresh air. Colin, however, hates fresh air.
Mary asks Colin if he wants her to go away, since he doesn't like people looking at him. He asks her to sit down and tell him about herself. They talk about India and Misselthwaite, and Colin shows her his beautiful books. Colin says that everyone must please him, as nobody believes he's going to grow up. He asks Mary's age, and Mary says that they're both ten—she knows this because he was born at the same time that Mr. Craven locked the garden door and buried the key. This interests Colin, but Mary evades his questions about the garden. He insists that he can make the servants tell him all about it, and Mary realizes that Colin is very spoiled. She finds it strange, even though she used to be just as spoiled.
When Mary tries to not tell Colin about the secret garden, it shows that at this point, the garden seems too fragile to share with anyone else. Dickon is trustworthy because of his intimate connection to nature, but Colin represents the exact opposite: entitled, indoor control of a dangerous and masculine variety. The fact that Mary finds Colin's spoiled nature strange speaks to how far she's come since arriving at Misselthwaite, when being so spoiled was just how things were for her.
Mary asks if Colin thinks he's going to die. He indifferently says that he's heard people saying he won't live for his entire life. His doctor now is Mr. Craven's cousin, who stands to inherit Misselthwaite if Colin dies. When Mary asks if Colin wants to live, he says he doesn't, but he doesn't want to die either. He returns the conversation to the garden and says that he wants to see it and will make the servants take him into it. Mary is afraid that this will ruin everything, so she begs him to not do it, as that will make it so the garden isn't a secret anymore. The mention of a secret intrigues Colin, and Mary tells him that it would be wonderful if they could find the door, sneak in, and play secretly.
Colin's assessment of why he's going to die—he's heard people saying it all his life—shows how powerful it is to hear something over and over again, especially something negative. Note that he doesn't list a diagnosis or anything concrete to cure; he just knows he’s sickly because he's been told that he is. This suggests that these negative thoughts and sayings are just as dangerous as physical illness. Mary's attempts to draw Colin towards the secret element of the secret garden—without yet divulging what she knows—shows that she understands how compelling secrets are for children who have little independence.
Colin wants to know if the garden is dead, and Mary explains that the bulbs will live, but the roses are questionable. She tells him that spring is coming and tells him again how wonderful it would be if they could find the way into the secret garden, watch things grow, says that it'd be nicer if it could be a secret. Colin says this secret is more fun than the secret that he's not going to live. Mary suggests that they could find someone to push Colin's wheelchair. Colin dreamily says he likes this idea. Mary keeps talking to him about what the garden might look like.
Colin's interest in what's dead or alive in the garden mimics Mary's earlier curiosity about the exact same thing. This suggests that just like Mary, Colin is in some ways lifeless on the inside because of neglect and because he hasn't been outside much. His continued interest in the fact that the garden is a secret shows that he's realizing that having this secret will allow him to be independent and not rely on others for something.
Colin points to a pink curtain on the wall and when Colin asks her to, Mary pulls it. It pulls the curtain aside to reveal a painting of a laughing girl whose eyes look just like Colin's. Colin says that this is Mrs. Craven, and if she'd lived, he wouldn't be ill and Mr. Craven wouldn't hate him. Mary closes the curtain and asks why he has the curtain in the first place. Colin explains that the portrait smiles too much, and he wants to keep his mother for himself.
By pinning his illness and Mr. Craven's bad attitude on Mrs. Craven's death, Colin confirms that Misselthwaite Manor is still grieving her loss. This suggests that the growth that’s to come will allow everyone to finally recover from her death and, in doing so, be able to properly honor her memory.
Mary asks what Mrs. Medlock will think if she finds out that she's here. Colin says that he's going to tell Mrs. Medlock to make Mary come talk to him every day. After a moment, Colin decides that he's going to keep Mary a secret too. He explains that Martha is caring for him now while his nurse is away, and she'll tell Mary when to visit. Mary asks if she should leave now and offers to sing one of her Ayah's songs for Colin. She takes his hand, pats it, and sings a song in Hindustani. She leaves when he falls asleep.
By singing one of her Ayah's songs for Colin, Mary again shows that not everything that happened to her in India was bad; she just didn't know how to use any of it. Now that she's feeling more whole and alive, she can pay some of what she learned forward and share it with others, as she does here. This moment also emphasizes how Colin and Mary have both grown up without involved parental figures, instead on hired help. While it’s usually parents who sing to their children at bedtime, here Mary functions as a caregiver of sorts for Colin, singing a song she learned from her own caregiver.