Modern youth Xue Gang accidentally time-travels to the isolated city of Kucha besieged by Tibetans, and upon waking up is tied to the city wall as a spy. He uses a first-aid kit to debride and suture the severely wounded Anxi commander Guo Xin, winning trust, but sees the city out of grain and seventy thousand military and civilians drinking thin porridge reflecting their shadows. To find grain, he takes a bag of gems from the warehouse back to modern times, running into appraisal fees, cold shoulders from the auction house, and Zhang Lei's six-hundred-thousand price cut; refusing to sell cheap, he uses a credit card to buy rice, flour, and salt and send them back to the Tang Dynasty, only to be kidnapped by Zhang Lei's men. Relying on two-realm travel, borrowed Tang army armor and weapons, he single-handedly subdues the kidnappers, extracts the mastermind, and turns the twenty thousand deposit into grain funds. The way out for seventy thousand military and civilians has just begun.