Beyond her canonical novel A Wrinkle in Time, Madeline L’Engle, who would have celebrated her birthday yesterday, created one of the most complex, interconnected literary universes committed to paper. The author was a religious Christian, but unlike C.S. Lewis adhered to an ultra-liberal strain of her faith that, as manifested in her novels, has gotten her books in hot water with school boards across the country.

L’Engle’s three main YA series feature the Murry family (Wrinkle protagonist Meg and her siblings), the O’Keefe clan (Meg and Calvin’s daughter Polly), and the Austin family. Unlike the universe-hopping Murrys and O’Keefes, the Austins don’t travel through tesseracts to other times or enter each other’s cells, but there are so many characters that go back and forth between the three series — including cute potential boyfriends Adam Eddington and Zachary Grey — that they all essentially comprise one expanded universe, encompassing many genres: realism, fantasy, murder mysteries, and science fiction.

One of the benefits of L’Engle’s need to revisit characters over and over again is the peek that readers get at their fates. Meg Murry, for instance, the precocious nerd-girl heroine of A Wrinkle in Time, ends up the mother to a whole brood of kids, with some serious regrets about her career — while her husband, Wrinkle‘s jock Calvin O’Keefe, is a famous scientist. Subtle gender oppression is real, and cloyingly happy endings are elusive. L’Engle’s novels frequently deal with death, religion, and sexuality, which keeps them on many banned books lists, decades later. They’re fantasy stories, but not fairy tales.

Here is a loose ranking of all the books in this expanded universe, from “you absolutely must read it if you missed it” to “read it only if you’re obsessed with the author’s work.” (Also worth exploring: L’Engle’s darker, sophisticated grown-up novels.)

1. A Ring of Endless Light

The commonly cited reason that this novel is the best L’Engle is: dolphins! And yes, our heroine Vicky Austin does communicate with intelligent dolphins. But this is also the ultimate YA book about falling in love and facing death — and also being at the beach for the summer, which is a third important YA theme. Rather than tackling the themes metaphorically, L’Engle goes right for it in this wondrous book that will make you weep and feel glad to be alive at the same time.

2. A Wrinkle in Time

The classic novel that launched L’Engle’s career was rejected from dozens of publishers before it found a home, and audience, and its iconic status. Meg Murry, with those pesky glasses of hers, travels in a world that’s a mix of science fiction, fantasy (L’Engle called it “science fantasy”), and teenage angst about family ties and love. A Wrinkle in Time works because, and despite, its strangeness.

3. A Swiftly Tilting Planet

The third novel in the Wrinkle in Time family (the Murry family books), this one mostly features Meg’s preternaturally gifted little brother, Charles Wallace. The two communicate telepathically by “kything” (which sounds weirdly like Skyping) as he travels by unicorn inside other people’s bodies. Again: weird, but perfect.

4. An Acceptable Time

Meg Murry’s daughter, Polyhymnia or Polly, is usually having prosaic adventures involving making out with guys or getting caught up in international intrigue. But in this one, she too time-travels, thanks perhaps to the mystic vibes in her grandparents’ Connecticut house, the same place where Meg once caught a tesseract in A Wrinkle In Time. Her journey back through the history of the People of the Wind is lyrical and brings to the fore L’Engle’s themes of love, courage, and forgiveness.

5. The Moon By Night

Perhaps L’Engle’s most simple, traditional teen-girl romance. No telepathy, no time-travel, just Vicky Austin on a cross-country road-trip with her family, two potential boyfriends who keep showing up (including Zachary Grey, who also figures heavily in A Ring of Endless Light and an Acceptable Time), and her own growing and changing sense of self and belonging.

6. A Wind in the Door

This is the mitochondria one, for those who don’t remember. The second Meg Murry adventure, this one finds her going inside Charles Wallace’s mitochondria (along with an alien/angel named Proginoskes), which have been inhabited by evil beings called Ecthroi.

7. Meet The Austins

The first Austin family novel. We meet Vicky Austin when she’s a wee lass, dealing with sibling rivalry and a new addition to her household. A winning introduction to the heroine many of us L’Engle fans love most.

8. A House Like a Lotus

Sex! And lesbianism! For young Polly O’Keefe, it’s quite the summer of discovery. Decades after her writing career started, L’Engle had more freedom to explore racier topics. Bonus points for an honest depiction of sexuality (which L’Engle didn’t shy away from in our her adult books), and a generally LGBT-friendly plot, but demerits for that plot taking a melodramatic and slightly problematic turn. Still worth reading, though.

9. Troubling a Star

After A Ring of Endless Light’s perfect, dolphin-streaked ending, it’s hard to imagine returning to Vicky Austin and Adam Eddington satisfactorily — but it’s also hard to imagine never returning to them at all. This sequel finds them traveling to Antarctica, with an almost Agatha Christie-like setup, full of allies and nemeses and intrigue. But the most intriguing question of all is: does Adam love Vicky the way she loves him?

10. The Arm of the Starfish

This is Adam’s book, and he’s a younger teenager, hanging out with the O’Keefe’s instead of the Austins (see how confusing everything gets?) Spying, secrets, deaths, and early, doomed romance. Don’t worry, Adam, Vicky is around the corner.

11. The Young Unicorns

Another of L’Engle’s conspiracy and intrigue novels, this one involves the Austin family, but more peripherally. It’s notable for a wonderful exploration of New York City, taking place in and around and beneath L’Engle’s beloved St. John the Divine cathedral in Morningside Heights.

12. Many Waters

The Murry twins, Sandy and Denys, are the normal ones compared to Meg and Charles Wallace, but in this religion-heavy installment, they have their own time-traveling adventure, right back into the Bible. There, they hang out with Noah’s extremely sexy family before the flood comes.

13. Dragons in the Water

Kidnapping, wild boars, murders and ancestral prophesies, and an early appearance by Polly O’Keefe are the notable features of this mystery novel, the weakest of a very strong bunch.