I stepped into the Poison Garden. Again, the feeling of ice water being poured down my throat caught me by surprise. The icy hot feeling stung at first but faded faster than it had during my previous visit. I swallowed hard. The tingling sensation lingered, but it didn’t hurt.

I slowly approached the rear wall. Treetops pushed down through the metal arches overhead. The wall was covered in poison ivy and Devil’s Pet so thick I could barely see the stones underneath. I touched the leaves, testing my immunity once again.

As my fingers grazed the foliage, vines shot out and twisted themselves around my wrists. I yanked my hand back, but they only gripped me harder. The long, toothlike spikes flattened themselves, lying against my skin but not puncturing it. My heart galloped into a furious rhythm as I tried to disentangle myself. Some of the purple leaves came off in the struggle but bloomed again under my touch. Another tendril encircled my waist and squeezed me so hard I couldn’t breathe. They dragged me across the ground, knocking my glasses off, then held me upright, my feet dangling above the ground.

“Stop!” I cried out.

The poisonous vines loosened their grip, sitting me down gently but not letting go. The Devil’s Pet and poison ivy parted like a theater curtain in front of me. There, in the stone wall, was a rusted metal door. At its center was a coat of arms or crest of some kind.

The Devil’s Pet unfurled, releasing me from its grip. I rubbed my aching wrists. A single curl of ivy slithered along the ground. It sprouted three skinny tendrils and used them like fingers to pick up my glasses and hand them back to me.

“Uh, thanks?” I didn’t know what else to say, so I wiped my lenses clean on the bottom edge of my shirt and moved closer to the newly revealed door to examine the symbol.

In the center was a woman’s face or—as I realized leaning in—three faces. One stared out from the center and the other two were turned to either side. Above the faces sat a crown of intertwined vines. All of this was rendered within a shield-shaped border that was encircled by tendrils of plants and curling leaves. At the very top, a key crossed by two torches was emblazoned in intricate detail.

The backplate where the keyhole sat was beautifully carved with a swirling pattern that reminded me of the Devil’s Pet.

I pulled out my keys and tried all three of them in the lock with no luck. I stepped away from the door and the vines fell back into place, concealing the door completely.

There hadn’t been any mention of another key in Circe’s letters, but she had said that everything I needed to know could be found in the house. Maybe the key was in there somewhere. I heaved an exhausted sigh as I pictured the endless piles of newspapers and magazines, drawers stuffed with knickknacks, and closets as big as our apartment back home. I didn’t even know where to start.

Wondering what was behind the door in the rear of the Poison Garden gnawed at me as I sifted through drawer after drawer, cabinet after cabinet. Questions crept into my head and twisted themselves around every idea I had. I couldn’t stop thinking about what could be behind it and why, in a garden full of plants that would kill someone who wasn’t like me, it needed to be locked behind a steel door that looked like it belonged in a bank vault.

I checked the safe one more time to make sure I hadn’t missed anything and took pictures of the pages in the big book so I’d know how to care for plants in the Poison Garden that I didn’t recognize. Mom and Mo had moved a bunch of trash out of the turret, so I examined the titles on the shelves one by one, checking between their pages for hidden spaces where someone might keep a key to a creepy door in a walled garden in the middle of the woods.

The books on the back shelf were older than the ones near the front. Their covers were made from leather, their pages yellowed and fragile. I took down a small, tattered book that looked in worse shape than most of the others. On its face was the word “Medea,” and in subscript, the name “Seneca.” I opened the cover and read from one of the pages.

“O gods! Vengeance! Come to me now, I beg, and help me . . .”

I skimmed through the rest of the book. I’d seen Hercules enough times to recognize some of the characters, like Jason, leader of the Argonauts, manning the ship called the Argo. But the main character in the tale seemed to be Medea, the woman from the paintings hanging in the turret.

I set the book aside and continued to look through the shelves. There were more old books, some encased in plastic and falling apart at the seams, and stacks of loose pages. I came to a section full of a half dozen identical bindings. Each leather-bound volume was filled with lists of herbs and plants, all with detailed instructions on their various uses and care. Every herb, plant, tree, or shrub I could think of was detailed, along with dozens of others I didn’t recognize. Next to each of them were instructions for their use. The entire tome was dedicated to the making of herbal remedies for ailments ranging from PMS to arthritis. There were salves for bruises and rashes, tinctures for upset stomachs and headaches. I put the books back on the shelf and took the copy of Medea with me to the table in the center of the room to read.

I spent a half hour skimming through it. Medea was a woman scorned, so full of anger and rage that she plotted against her unfaithful husband by concocting a poison to kill his new lover. I was so unsettled by the description of Medea killing her own children to hurt Jason that I had to close the book and refocus. The story made it seem like Jason was the person the reader should pity, but the tragic figure was clearly Medea. What kind of person would do that to their own kids?

I gathered some of the other books from the back shelves—­Metamorphoses, Fabulae, Heroides—and took them to my room.

I spent the rest of the late afternoon reading and making notes. Every single book that mentioned Medea was marked up, passages underlined with pencil, notes scribbled in the margins. She was a devotee of a goddess called Hecate, Guardian of the Crossroads, Keeper of the Keys. She had a hundred names, and her mythology went back even further than Medea’s, to a time before the gods in Greek myths even existed. Hecate and Medea were always mentioned in connection with each other.

Mo stuck her head in my room. “You okay? You’ve been in here awhile.”

I checked my phone. It was almost eight o’clock.

“I lost track of what time it was.” I jumped off the bed. “I told Mom I was gonna help clean. I’m sorry, I got caught up in these old books I found.”