Why did Francis Scott Key go to Baltimore harbor?

Key was an attorney by profession. He was attempting to negotiate the release of Dr. William Beanes who was detained by the British and held aboard a ship of the invasion fleet for his part in rounding up British stragglers and putting them in the local jail for looting. Key and a colleague were able to locate the British fleet commander and effect the release of Dr. Beanes but all were detained by the British who felt Key and the other Americans had learned too much about British dispositions, strength and plans to safely release him and his party until the engagement at Baltimore was completed.