This is a DNF review. Only 40% was read, the rest was skimmed. 
 My initial expectation of PLUS ONE was that it was basically going to be like a Romeo & Juliet retelling, or another THESE BROKEN STARS. Apart from the forbidden romance, this book could not be more different. 
 PLUS ONE started out confusing, and only got more confusing. Being thrown right into the story where terminology and new words are being thrown around is no fun. It was frustrating not knowing any background or having any explanations until later in the book. I even would have preferred an info-dump to ignorance. 
 I'm still not entirely sure what the book was about. I read almost halfway through, and I'm still pretty sure it's about babies. No joke. Secret babies, stolen babies, misplaced babies, and super special babies. But mostly just people stealing babies. 
 On my way to steal yo baby. 
 The characters are pretty eccentric, and the dynamic they have together is even more weird. Because of that aspect, I did not buy into the romance. At all. When the love interest was first introduced I didn't even think he was going to be the love interest, I had no clue. Trust me, that's not a good thing. It was more of a "this guy can't possibly be the love interest. Please don't let him be the love interest." 
 The writing itself is very descriptive and easy to read. It's... well, it's pretty. 
 "The bridge was geologically ancient, an impassive observer, surrounded by life that was fleeting in comparison: trees that would only survive hundreds of years, tourists who would only live decades, insects that would thrive only for weeks." 
 So if unconventional characters and ... babies? are your thing, PLUS ONE is definitely for you. On a more serious note, the concept and writing are two huge positives but I wouldn't put too much weight on the other aspects of this book.