Meredith Grey is confused when weird patients come to her hospital. They have odd symptoms like color-changing rashes, floating in the air, and talking in strange languages. Two oddly dressed people show up saying they're "medical consultants" from London. Meredith doesn't believe them until Harry uses magic to stop a patient's glowing tears from affecting others.

In the hospital meeting room, Hermione tells Meredith, who doesn't believe her, that a magic experiment that went badly has made a special germ that makes both magic and normal people sick. "Medicine can only do so much, just like magic," Hermione says. Meredith answers back, "I work with science and facts, not wands and spells." Harry steps in to help, saying they should work together instead of arguing about which way is better.

Working late at night in the lab, Hermione is impressed by how careful Meredith is when taking tiny pieces of tissue from sick patients. When Hermione uses a magic spell on Meredith's well-prepared glass slides, they can finally see the shiny, pretty-looking germ that keeps changing its shape. "It changes with feelings," Meredith suddenly understands, noticing something important that even Harry and Hermione hadn't figured out.

A child patient's condition deteriorates rapidly, with magical energy creating dangerous pressure in her brain. In the OR, Meredith works fearlessly alongside Harry, who maintains a stabilizing charm while she performs an emergency procedure. Their seamless teamwork saves the child, earning Harry's profound respect for Muggle medicine and Meredith's growing acceptance that magic might be just another form of science she doesn't yet understand.

In a quiet break in the doctors' rest room, the three talk about their lives. Meredith tells them about her mother dying from Alzheimer's disease. Harry talks about growing up with no parents. Hermione shares how she changed her parents' memories to keep them safe. "Sometimes I wish I could do that to myself," Meredith says, "make myself forget the hard parts of my life." Hermione looks thoughtful when she hears this, but doesn't say anything.

After working together for many days, they create a special cure, a magic potion that has to be put right onto the sick organs during surgery. While Meredith does the careful operations, Harry and Hermione send magic through special tools they prepared. The patients start getting better, and everyone at the hospital thinks it's because of a new test medicine. They don't know that magic was used to help cure the patients.

After they fix the problem, Hermione brings up a tough issue, "Our magic rules say that regular people can't know about magic." Harry says Meredith deserves to keep knowing because they trust her. Meredith is having a hard time fitting what she saw with what she knows about science. "Some patients said they felt like they were dreaming when they were sick," Hermione says thoughtfully. "Maybe that's how everyone should remember what happened."

On their last night, after healing everyone, Hermione casts a memory spell on sleeping Meredith. The next morning, Meredith only remembers the magic as a fading dream. She finds a note, "Some mysteries in medicine remain beautiful even when unexplained. Thank you. H & H."