At 2:45 on a Sunday afternoon, Jaclyn Pryor is wearing a suit and a yalmulke, running down an avenue in Hyde Park. Eight white Volvos trail behind her. A squadron of brides—including at least one man—look to the sky and take off running from an adjacent front lawn, joining the procession. Passers-by stand and gawk. Inside each Volvo, Pachelbel’s Canon plays. It is a perfect moment....