The story takes place in ancient times when mountains and rivers were broken. The protagonist Su Ran was originally a civil servant in the court, but was demoted to the border for his uprightness. At this time, the northern cavalry broke through Bianliang. He was holding a broken military talisman in his hand. He was in an isolated city with only 300 old and weak soldiers around him. Inside the city were the orphans of the displaced royal family. Outside the city, 100,000 enemy invaders were watching with eager eyes, and there were no reinforcements or food. At the critical moment, Su Ran activated the "Strongest City Defense System", which assisted him in the mode of "publishing tasks - completing challenges - receiving rewards - unlocking stronger abilities". The enemy continues to launch attacks and spreads false news that reinforcements have arrived to disrupt the morale of the army. Su Ran is faced with the dilemma of accepting the persuasion to surrender and gaining glory and wealth, or holding on to the isolated city to protect the orphans of the royal family. He relied on the knowledge given by the system and his own resourcefulness to resolve crises time after time. However, every victory was accompanied by the sacrifice of soldiers, which made him sad in his heart. In the end, Su Ran successfully defended the isolated city, but he also paid a heavy price and carved an unyielding legend in the history books.
