High in the sky above Earth is a most beautiful star, inhabited by a race of people who keep the heavens safe the Starlings. Their job, which they have done for as long as anyone can remember, is to help grant the wishes of humans. Wishes made on birthday candles, shooting stars, dandelions, wishbones, and coins tossed into fountains, just to name a few. As long as humans keep believing in wishes, the stars will keep shining in the sky and life, for Starlings and humans alike, will continue as they know it.

Book One begins as the incoming class arrives at Star Academy. Cassie is having some trouble fitting in, feeling homesick already. She's doubting herself a bit, wondering if she really even belongs in Star Academy. Plus she's not particularly fond of her roommate, who is a little too blunt for Cassie's taste. She has begun to retreat inside her shell a bit. The girls begin to take classes, meet new friends. Then, unexpectedly, twelve girls are summoned to the headmistress's office for a meeting. They soon discover that they have each done something remarkable in their first week and have been identified as truly special students. And something genuinely extraordinary is going to be asked of each of them as a result.

The headmistress explains that something unusual has been going on. Wishes are not being fulfilled as easily as they have been in the past. Humans are starting to disbelieve and make fewer wishes. Something drastic needs to be done. The twelve girls are given a special name: the Star Darlings. And it's up to them to find out why humans have stopped believing—and to fix it!