the more of these american girl mysteries i read, the more ludicrous they seem. i guess it must be challenging to come up with a plotline that is truly mysterious but also age-appropriate for a child. & at least this book involved more of a mystery than, "there's a polio epidemic & the girl in the next bunk over at sleepaway camp seems to have some health issues. wonder if it's polio?" (ie, secrets at camp nokomis).
rebecca is concerned about a rash of kidnappings sweeping new york city. someone is stealing babies left unattended outside shops & other such places (apparently this was a pretty common practice back in ye olden days) & ransoming them for thousands of dollars. the babies are often from poor families who have to beg friends & neighbors for donations to raise the ransoms & get their babies back. rebecca becomes even more suspicious when she realizes that her older brother snuck out of the apartment on the night that one baby was returned to its family.
but she is swiftly distracted when a new family moves into her building. they moved from a nearby tenement & the mom in the family developed an eye infection that is imperiling her vision. the father works two jobs to pay for her medical care, & they have a little baby named nora, who is screaming her head off when rebecca meets the family. various cousins & aunts & whatnot are also milling around, as well as another woman who lives in the neighborhood & offers to look after the baby while the family gets settled in. mrs. rubin takes the baby instead & she & rebecca notice the baby has a bad diaper rash & needs her nails trimmed. rebecca guesses that nora's parents didn't have time for these things, or maybe even didn't notice, with the mom's eyesight failing & everything.
they get the baby all spruced up & rebecca takes her to a nearby park. she makes the acquaintance of another young girl there, named francesca. francesca is also looking after a baby, her little sister. rebecca is spooked by a slightly older boy with a thick italian accent who looks a little too closely at nora & asks rebecca some mundane questions about her. rebecca thinks it's strange that a boy that age would pay any attention to a baby. she even wonders if he might be involved with the kidnappings that have been happening. when she sees her brother running around with the boy, she gets even more concerned. then the boy's dog runs off with nora's rattle & rebecca chases after it.
the next day, rebecca stops by to visit with the new family again. she notices that nora is cheerful & happy as a clam, compared to all the screaming & fussing she was doing the day before. she remembers that the baby that was with francesca was very calm & sweet. she checks nora's dress & finds a little embroidered horn on the hem, the same as the embroidered horn on francesca's little sister's dress (an italian charm to ward off the evil eye). she realizes that the babies must have been switched while she was chasing after the dog. she rushes out to find francesca & get her help to switch the babies back.
she discovers that francesca is the little sister of the boy who seemed so interested in nora the day before. when she finally finds francesca & tells her that the babies have been switched, francesca insists that it's not true & won't listen to rebecca. rebecca becomes concerned that francesca switched the babies on purpose--that maybe she is mixed up in the kidnappings as well (although switching babies is not really the same as kidnapping them & holding them for ransom). she also unearths other odd or unsettling information: her brother is running around in a "gang" of "bad boys". rebecca sees them steal lollipops from a local ice cream vender. she also sees the local woman who has offered to look after nora. she sees the woman drop a package of brand-new baby clothes in the trash, & she realizes that a stern-looking man in a hat saw rebecca remove them from the trash.
rebecca tells her mother about the babies being switched, hoping that she can lean on francesca to switch them back. mrs. rubin dismisses this, insisting that a mother always knows her own child, even if her eyesight isn't the best. but rebecca knows the sweet, quiet baby the neighbors have now is not the same fussy, screaming baby she took to the park. the new baby's nails need to be clipped again already & her diaper rash is completely gone. (i guess they needed this kind of actual physical evidence to forestall arguments that sometimes babies cry & sometimes they're cheerful & it doesn't mean they are different babies.)
finally rebecca tracks down francesca's mother, who is sitting outside bouncing a fretful, crying baby. she confirms that the baby is her own daughter. rebecca starts hooting & hollering about how the babies have been switched. by this point, she thinks francesca's entire family is running some kind of very confusing baby-switching/kidnapping ring & she bolts over to a cop & requests his assistance in switching the babies back. francesca appears & seems very determined in her insistence that the babies have not been switched & that rebecca should drop it. then nora's father turns up & he knows francesca's family. apparently they live in the tenement building that he & his family just moved out of. rebecca is even more confused but she drops her kidnapping assumptions when she sees nora's father greeting the italian baby with no recognition that it may be his own child.
finally francesca explains: her brother likes to play pranks. while nora's family was moving out of the tenement, they asked francesca to look after nora for a little while. she was also looking after her little sister. something happened to nora's dress, so francesca dressed nora in one of her sister's spare dresses. then she was called away & asked her brother to keep an eye on the babies for a minute. he did, & thought it would be a funny prank on francesca to place their sister in nora's pram & nora in their sister's bed. unfortunately for him, nora's aunt & uncle came to pick her up & take her to the new apartment before francesca realized the babies had been switched. they weren't familiar with nora & didn't realize they were taking the wrong baby, & francesca didn't realize it until it was too late. she machinated a meeting with rebecca & nora in the park (using her older brother as a look-out, hence his strange interest in the baby) & switched them when rebecca's back was turned. but because rebecca was introduced to the impostor baby as nora, she didn't realize that francesca was switching the babies BACK. they decide not to tell anyone what happened because the babies are back with the right families & that's what counts. i think francesca & her brother are pretty lucky that nora's family wasn't moving to, like, des moines. switching babies is no joke!
rebecca is walking through the park when she suddenly realizes that the woman who had offered to look after nora & the stern man in the hat are the real kidnappers. she happens to run into them almost immediately & they grab her & try to hustle her out of the park. at first she goes meekly, rememering what her mother says about how "ladies don't draw attention to themselves". then she remembers what her grandmother says about how ladies are loud if they need to be & she starts hollering. francesca's brother helps catch the kidnappers, earning the goodwill of the police for once, & rebecca breaks the kidnapping case (via that old chestnut, deux ex machina, basically). her brother admits that he's been sneaking out at night to build the family a sukkah on the roof of their building.
rebecca came across as a bit of a meddlesome drama queen in this book. she could have saved herself a lot of trouble if she just stayed out of other people's business. there was also a weird scene in which francesca's mother is holding a baby, nora is in her pram, & rebecca "looks at the baby in her arms". i was super confused by that because i couldn't figure out how a third baby came on to the scene. i read it like ten times before i concluded that it was just an especially egregious editing/continuity error.