Dr. Craven is relieved when Mary, Colin, and Dickon return. When Colin announces that he's going out in the morning and in the afternoon tomorrow, Dr. Craven insists that he shouldn't. Colin, however, holds firm. Having been at Misselthwaite for a while, Mary now understands that the manners she arrived with were horrid. She recognizes that Colin's manners are much like hers once were, and so after Dr. Craven leaves, she says that she feels sorry for Dr. Craven for having to to put up with Colin's rudeness for the last ten years. Colin seems unperturbed to learn that he's rude, even when Mary says that Dr. Craven would be justified in slapping Colin.
Mary's newfound ability to recognize Colin's terrible manners for what they are (and, by extension, gain a clearer picture of her earlier behavior) speaks to the superiority of the way she lives at Misselthwaite in comparison to how she lived in India. She now recognizes that even though he's already in England, Colin behaves as though he's in India and owns everything. With this, Mary is again able to act as a mirror and show Colin the error of his ways.
When Colin reminds Mary that nobody would dare slap him, she points out that nobody wanted to upset him because he was so ill. She continues that being so spoiled has made him strange. Being called strange is something that seems to disturb Colin, though Mary assures him that both she and Ben Weatherstaff are strange, but less so since discovering the garden. Colin vows to not be so strange and to do so, he'll go daily to the garden where there's Magic. They decide that even if the Magic isn't real, they'll pretend it is.
By deciding that the garden and Magic are the things that are going to help him be less strange, Colin is essentially recognizing the power of being in nature and thinking positive thoughts (which is essentially all Magic is). When they decide to pretend that the Magic is real, it suggests that the power of it lies in the individual, not in an actual higher power.
In the following months the Magic seems real as Dickon, Mary, Colin, and Ben Weatherstaff watch the garden come to life. Flowers bloom, and Ben tells the children about the flowers that Mrs. Craven liked. The roses develop buds that eventually turn into hundreds of blossoms. Colin decides that he can see things growing and blooming and enjoys watching the wildlife. When Colin learns that Mary "worked a spell" when he stood the first time, he's excited. He reasons that to start using Magic, one must say that nice things are going to happen until they happen.
The spell that Colin refers to was Mary's muttering of "you can do it" over and over again while Colin was attempting to stand up, which is positive thinking at its most basic. This suggests that the person in question doesn't need to be the one doing the positive thinking to be affected by it, which will become important later. It implies that positive thinking has implications beyond an individual or indeed, beyond the garden.
The next morning, Colin summons Ben Weatherstaff and tells him that he wants him to stand with Dickon and Mary and listen to him speak about important things. Colin declares that he's going to grow up to be a scientist, but he's starting now with an experiment. He says that he's going to experiment with Magic and says that Dickon has Magic because he's an animal charmer. Colin continues that the garden used to look dead, but now things are alive, and this must be the work of Magic. He says that Magic made him happy for the first time, made him stand, and made him believe he's gong to grow to adulthood. He mentions Mary's spell and says that every morning, he's going to say that the Magic is in him and is making him well. He asks the others to do the same.
Colin's practice speech cements the novel's assertion that the things the children learn in the garden aren't things that they can or should keep to themselves. Rather, just as Colin frames this as being a speech on his scientific experiment, one that in the future he might give to a panel of other scientists, it suggests that the whole point of making these gains is to share them. Then, by suggesting that he perform a chant every morning, it indicates that a good way to continue to think positively is to make it part of a routine.
Colin insists that if they repeat this often enough, it'll become second nature. Mary notes that holy people in India did much the same thing, and Ben Weatherstaff says he's heard of that happening too—a local woman called her husband a drunk so many times, he beat her and then got drunk. Colin thinks for a moment and then says that the woman used the wrong kind of Magic, and it made her husband violent. Ben calls Colin clever for this insight.
By tying the idea of Magic to Indian faith traditions and to local problems, the novel takes a universalist stance and suggests that Magic is not something that can be attributed to a single faith. While Colin's assessment of the roots of domestic violence is problematic, it nonetheless shows him experimenting with what he believes and trying to make it fit in a way that makes sense.
Dickon looks curious and delighted and tells Colin that he thinks the experiment will work. He suggests they begin immediately, so Colin arranges everyone under a tree. Ben feels as though he's in a "prayer-meeting," but for once, he doesn't resent being there. Dickon's creatures settle themselves nearby. Colin asks everyone to sway and when Ben insists that his rheumatics won't let him, Colin insists that the Magic will cure the rheumatics. Colin begins to chant that the sunshine, the growing plants, and being alive are all Magic. He asks the Magic to help and everyone feels as though they're in a trance. After many repetitions, Colin announces that he's going to walk around the garden. This jerks Ben out of his nap.
Ben's sense of being in church reinforces the religious overtones of this chanting circle, but his lack of resentment suggests that this system of Magic and positive thinking is more palatable than organized religion. When Colin insists that Magic will cure Ben's arthritis, it shows how deeply he believes in Magic to cure things that are truly physical ailments and not something that takes place in one's head, as Colin's illness did. Notably, the novel never says one way or another if this works for Ben, suggesting there may be limits on what Magic can do, but leaving room for hope, too.
Mary, Dickon, and Colin lead the way, with Ben Weatherstaff and the creatures following. They move slowly around the garden and after a while, Colin walks unassisted. He continues to say that the Magic is in him and is making him strong. When they return to the tree, Colin declares that he's made his first scientific discovery—but says that Dr. Craven and the household aren't to know about it. He doesn't want people whispering and doesn't want Mr. Craven to find out until Colin can walk up to him and tell him he's well. The narrator notes that Colin has now made up his mind to get well, which is more than half the battle. Ben suggests that Colin will be a boxing champion by the end of the week, which Colin finds disrespectful. Privately, Ben is thrilled that Colin is strong enough to reprimand him.
By shifting his thinking to have a specific goal and a specific end date (telling Mr. Craven and his time of return, respectively), the novel reminds the reader that effective secrets are one that have end dates. Unlike keeping Colin's existence a secret or the secret garden locked up, which were supposed to continue indefinitely and also weren't effective, Colin's secret is construed as positive. It allows him to feel independent and in control of his future, while wanting his father's affection shows that he's becoming ready to leave the proverbial nest.