A modern doctor receives a message from an unknown sender.

The name is Lee Hyang. A quick search reveals the impossible truth. It is the birth name of King Munjong, the fifth ruler of Joseon.

The king speaks of relentless fever and a cough that never fades. Tuberculosis, by modern standards. A death sentence in his time.

At first, it seems like a prank. Then the impossible begins.

Every piece of medical advice sent through the mysterious messenger app “Gatong” starts to take effect. Prescriptions change the past. Treatments alter the king’s condition.

And the Annals of the Joseon Dynasty begin to update in real time.

History is no longer fixed.

As the doctor guides a king through illness, he unknowingly begins to reshape an entire era. Coups shift, power balances change, and a fragile timeline bends with every message sent.

But each change carries consequences.

The past is changing.

And so is the present.

Saving one king might rewrite the fate of a nation.