When Washington D.C. was attacked and burned in August 1814, the British felt secure to start a systematic campaign of attacking the major cities of the United States. To them, the collapse of authority in Washington meant there would be little organized resistance elsewhere. So Admiral Cockburn (who burned the White House - supposedly saying, "Shall this haven of Yankee democracy be burned?" as he stood on the dining room table) and General Robert Ross decided to go up the coast and attack Baltimore.
The attack was to turn out easier said than done. When Washington fell, the fault was in the confidence placed in General James Winder by President Madison and Secretary of War James Monroe. Winder was an incompetent. But the local forces around Baltimore were not regular army like Winder, but local militia who knew the terrain. So when General Ross did a private reconnaissance of the outskirts of Baltimore, he was shot and killed. This did not help the morale of British troops.*
(*Ross is one of three British commanders who died in the War of 1812. The others were Isaac Brock and Edward Parkingham. Parkingham was the commander of the British at New Orleans, whose death in that battle was one more disaster in an encounter that cost 2,000 British lives - and barely as many as 1/20th that number of Americans. Brock, the "luckiest" of these three officers, died at the Battle of Queenstown Heights (near present day Toronto), but he won that battle, and is remembered as a national hero who saved Canada to this day in that country.)
The British had been able to capture some civilian stragglers, including a Dr. Beanes (played here by Griff Barnett). One of Beanes' neighbors, Mr. Francis Scott Key (Donald Murphey) went to get the doctor released from the British. Key had to board a British ship in Cockburn's fleet to see Beanes, but then the attack on the harbor of Baltimore began - suddenly Key was told that he as well as Beanes had to be considered prisoners of war until the battle ended. So Key watched the attack of the fleet on the harbor. The attack was blunted and defeated by the American defenders in Fort McHenry. Key had to stay on-board until the following morning. He had been watching and jotting down ideas - and he eventually wrote these up in the poem called "The Star Spangled Banner", referring to the American flag over the fort that never came down in the battle, and "was still there" at the end. The poem, set to an old British drinking song that was in the public domain, eventually became our national anthem.