I have one sister, and growing up, we fought frequently. As much fighting as we did, we never went so far as to actually try to murder one another like the sirens in Lullaby did. If I had to spend a couple of thousands of years in close proximity with a couple of sisters, completely with insanity and jealousy and rivalry, I'm pretty sure I wouldn't make it either. 
 I have a theory as to why there aren't any more mermaids and sirens in the world these days. It's not because they're mythical creatures, it's because they either kill each other until there are none left, or went extinct from their own stupidity. Natural selection has its uses. 
 Sirens are like pandas, too dumb to actually survive on their own; I actually think pandas have an evolutionary advantage, since they make humans want to take care of them. They're too lazy and stupid to find their own food and to actually recreate, so they just sit there, look cute, and have us silly humans coo over them and do everything for them short of giving them panda Viagra...actually, scratch that, I think zoologists have done that too. 
 I do have a point to make in this review, I swear. 
 Sirens are beautiful, seductive...they also get humans into doing shit for them through their song and through seduction, but instead of keeping a low profile, they kill people in really obvious manners, grab ostentatious places to live, and generally make themselves a walking target for angry villagers to burn them out of town. I can't recall reading too many books and films about mermaids and sirens, but they're generally TSTL, and the myth is further perpetuated through Amanda Hocking's Watersong series. 
 In this installment of the series, Gemma is now a siren after drinking Penn's concoction. She goes with the other sirens to live in a sumptuous beachside mansion, whose gorgeous owner, Sawyer, has been seduced by Penn into giving them carte blanche to everything he owns (see my note above on blending in, this is not inconspicuous in the least). 
 Meanwhile, Gemma's sister Harper, her boyfriend Alex, and Harper's love interest Daniel are doing everything they can to look for her, including involving Harper's coworker Marcy, who is the most gullible person on the planet. Harper's almost-brain-dead mother somehow mysteriously knows that Gemma is with the sirens, and her dad Brian is being emo and moping around the house, never mind that he has one remaining daughter to take care of, a job that he needs to go to in order to keep the health insurance their family desperately needs to keep their mother in the health care facility. 
 None of the characters in the book act in a realistic manner. The actions, speech, and overall feel of the book is very stiff. Harper isn't much of a character, she lacks personality in general, I understand that her character is supposed to be the "serious" one keeping the family together, but it seems like there's no personality to her at all. Gemma is too goody-goody and TSTL to be a good siren; the other sirens supposedly chose her, but they really picked a piss-poor candidate. If I were to choose someone to join a sorority, for example, I'd pick someone with a similar personality, who is somewhat malleable, and with whom I'd get along, not someone who hates the very nature of who I am and who resists everything I stand for. 
 There are gaping holes in the plot, such as the inclusion of Greek mythology...if there were Greek gods and goddesses, where are they now? You can't include one element of a mythology and conveniently leave out the rest. The book ends too suddenly, and too easily, given what we know of Penn's personality. The most evil of the sirens should not have acted the way she did.