On first sight, Calvin O'Keefe might not seem to have much in common with Meg and Charles Wallace. After all, he's in the popular crowd, on the basketball team, and so good in school he's skipped a couple of grades. Despite his outward success at all the things that Meg fails at and Charles Wallace cares little about, Calvin considers himself a "sport" (2.99), an odd man out. While Meg and Charles Wallace are misunderstood by their community at large, it's his own family where Calvin doesn't fit in.
"I don't know why I call her when I don't come home," Calvin said, his voice bitter. "She wouldn't notice." He sighed and dialed. "Ma?" he said. "Oh, Hinky. Tell Ma I won't be home till late. Now don't forget. I don't want to be locked out again." He hung up, looked at Meg. "Do you know how lucky you are?" (3.11)
Calvin's family has so little concern for him that they don't even notice if he's home or not. Calvin's situation can be seen as the mirror image of Meg's: he's accepted in public, disregarded at home, while she's got the opposite problem. Calvin's entrance into the novel, and into Meg's life, suggests that the appearance of happy normality can be deceiving – and that Meg has a lot more going for her than she might think.
Throughout the first part of their journey with the Mrs. Ws, Calvin takes on the role of Meg's protector, and Meg welcomes his concern. After the Happy Medium shows them Calvin's mother, however, the tables turn, if only for a moment.
If anyone had told her only the day before that she, Meg, the snaggle-toothed, the myopic, the clumsy, would be taking a boy's hand to offer him comfort and strength, particularly a popular and important boy like Calvin, the idea would have been beyond her comprehension. But now it seemed as natural to want to help and protect Calvin as it did Charles Wallace. (6.46)
This switcheroo reinforces the message that appearances can be deceiving, and also suggests that Meg has hidden reserves of strength if she only would step up to the plate. (We'll just try to ignore the weirdness of seeing potential boyfriend material as a little brother.) Calvin's admiration of Meg gives a boost to her self-worth, and his vulnerability gives her a chance to use her newfound confidence.
When the Mrs. Ws send the kids off to do battle against the giant brain, Mrs. Whatsit's power-up to Calvin is to strengthen his natural talent for communication. While even Calvin doesn't have much luck getting through to the man with the red eyes, he does almost manage to break through the formidable barriers to communication with Chucky, the robot-like Charles Wallace.
Again Charles shuddered. And then it was as though an invisible hand had smacked against his chest and knocked him to the ground, and the stare with which Calvin had held him was broken. Charles sat there on the floor of the corridor whimpering, not a small boy's sound, but a fearful, animal noise. (9.30)
There's some serious power in communication, apparently. By making Calvin's words deliver the equivalent of a punch to the gut – and have more of an effect on Chucky than Calvin's literal tackling of him did earlier – the novel suggests that language can trump violence when it comes to having an impact.
When it becomes clear that Mrs. Whatsit is going to take Meg back to Camazotz, Calvin starts to take his self-given role as Meg's protector a little too seriously.
Calvin jumped down. "Maybe IT's right about you! Or maybe you're in league with IT. I'm the one to go if anybody goes! Why did you bring me along at all? To take care of Meg! You said so yourself!"
"But you have done that," Mrs. Whatsit assured him.
"I haven't done anything!" Calvin shouted. "You can't send Meg! I won't allow it! I'll put my foot down! I won't permit it!" (12.40-42)
Looks like someone's been reading Edward Cullen's How to Be a Controlling, Possessive Boyfriend in 10 Easy Steps. Calvin's arrogant assumption that he has the right to tell Meg what she can and can't do is rightly shot down by Mrs. Whatsit. Later, his insistence that Meg is too "backward" to go by herself (12.51) earns a scathing come-back from Meg herself. Is Calvin showing his true colors under pressure, or is fear that something might happen to Meg making him a little crazy? Looking at his behavior in the rest of the book helps us answer that question. Calvin is mostly pretty respectful of Meg, so hopefully this is just an example of love and fear making him do the wacky. (If we were Meg, though, we'd be on the lookout for future outbreaks of Edwarditis.)
What will happen to Calvin once they all make it safely back to Earth? The novel doesn't tell us, but Mrs. Murry's pulling him into the group hug suggests that he's going to be an honorary member of the Murry family from now on.