The story ends — its very last words — with “twin swans,” a return to the beginning as evident bracketing:
Head bowed against the rain, [Robin] had no attention left to spare for the magnificent mansion past which she was walking, its rain specked windows facing the great river, its front doors engraved with twin swans. (p 647)
Brad Bellows told us, in a comment attached to Evan Willis’ post on the hermetic and mythological meaning of Lethal White, that “the paired swans Robin fails to notice in the final line, actually exist, on Swan House, built in 1876 by R.N. Shaw, overlooking the Thames.” Mr Willis in that post had suggested this might be Jonny Rokeby’s home in keeping with his theory that, per Leda and the Swan/Zeus mythology, that Strike’s mysterious paternity, the pairing of his super-groupie mother with the other-worldly rock-star, explains why Rokeby remains off-stage but ever-present. The myth holds that Leda has twins, two sets of twins actually, with two fathers for each set; Castor and Pollux are the off-spring of Leda with the swan who is Zeus and with the king of Sparta, her husband. Robin and Cormoran, great driver and former boxer, are the novel’s stand-in for Castor the horseman and Pollux the pugilist. [See the discussions of this mythology and the Strike mysteries in the Gray/Granger and Willis posts on the subject.]
While the predominant symbolism of the story is white horses, which occur so frequently that Strike remarks on it and Billy Knight laughs about it (pp 394, 496), white swans occur often enough, not only as the story’s framing brackets but in references to individual birds on signs (see Robin’s noting and overlooking the Swan pub sign on pp 56 and 166), that we are obliged to consider their meaning beyond markers of Leda mythology in which the books are set. Swans, as you might expect in a Rowling novel, have an alchemical meaning as well, one that we will explore after the jump.
Much has been said about the Christian themes, symbolism and allusions in Harry Potter, and indeed much remains to be said. In 
Get ready, dear readers in the United Kingdom, for the erudite nerdiness of 
“Professor Strand, which is your favorite Harry Potter movie?” a student asked recently as class began.
The story begins — its first words — at the Cunliffe wedding reception with a photographer trying to get a picture of the newlyweds that includes two swans in the pond behind them. The swans stubbornly refuse to come together, but, as soon as Robin rises to separate herself from Matt (with the intention of looking for Cormoran), they swim side by side. The clueless father of the groom observes, “You’d think the buggers were doing it on purpose” (p 3).