Charles keeps us in the dark for ages about the identity of his wife. He doesn’t even officially clue his reader into the fact that he's married; he just casually mentions that he has a wife and expects us to fill in the details. Finally we realize – through hearing her speak her own name over the telephone – that Mrs. Ryder is in fact Celia, Boy Mulcaster’s sister.
If you missed her introduction earlier in the novel, it’s understandable. We get only a brief second-hand description, courtesy of Mr. Samgrass:
"I shall miss the pretty creatures about the house – particularly one Celia; she is the sister of our old companion in adversity, Boy Mulcaster, and wonderfully unlike him. She has a bird-like style of conversation, pecking away at the subject in a way I find most engaging, and a school-monitor style of dress which I can only call 'saucy.'"
Remember that Charles is narrating this all in retrospect. The fact that he passes over this moment without the least bit of attention or care is a real indication of his feelings for his wife: complete apathy at best, utter disdain at the worst. (For comparison, think about the pages and pages Charles devotes to describing Julia’s every word and movement, even long before they get involved in Book Two.)
We can certainly confirm this assessment of Charles’s marriage when we see it first-hand aboard the ship on the Atlantic, based on his descriptions of his wife (whose name he still refuses to use). "[She] was adept in achieving such small advantages," he says of their large rooms on the ship, "first impressing the impressionable with her chic and my celebrity and, superiority once firmly established, changing quickly to a pose of almost flirtatious affability." She references Charles’s proposal to her, and his response is, "As I remember, you popped [the question]." He resentfully describes her attempt to "ingratiate" him with "two Hollywood magnates" she invited to the party which he seems to resent in itself.
This is really some brilliant characterization on Waugh’s part. Charles is never deliberately antagonistic towards his wife, but it’s painfully clear that he in no way loves her. He doesn’t even want to see their children! Just as Lord Marchmain "can barely be happy with Sebastian because he is [Lady Marchmain’s] son," so Charles can not be happy with his children, because they belong to a woman he hates. (There’s also a possibility that Charles’s first child, Johnjohn, isn’t his, since we find out that Celia has not been faithful.)
But is Charles’s disdain warranted? What’s so bad about Celia? She’s certainly nothing like Julia, that’s for sure. Read about this "Foil" in Shmoop’s "Character Role ID" and you’ll see what we’re talking about. Julia is smart, tough, and a formidable match for Charles, while Celia is overly-feminine and charming to the point of annoyance. In fact, Celia represents everything Anthony so vehemently warned Charles against – "creamy British charm." Charles recognizes this himself. When his wife speaks with her calm, aristocratic, charming way, he confesses that "throughout [his] married life, again and again, [he has] felt [his] bowels shrivel within [him] at the things she said." In fact, he doesn’t feel free of her charm until he "detects [her] in adultery." It’s almost as though she proved herself to be – like her brother – rather a degenerate, NOT the picture of perfect British charm after all. Conveniently, this gives Charles moral permission –at least in his mind – to pursue Julia without compunction.