Short answers, pulled from the story.
The Convention of Cintra was an agreement signed at the Palace of Queluz in Cintra on the 30th of August 1808. This treaty allowed French troops to evacuate from Portugal under specific terms negotiated by Sir Hew Dalrymple and François Kellerman.
The Royal Navy transported nearly 21,000 French soldiers from Portugal to Rochefort. These troops carried all their equipment and personal property during the journey without any loss occurring during this massive naval operation.
Sir Arthur Wellesley commanded the Anglo-Portuguese troops that cut off French retreat options after defeating Jean-Andoche Junot's forces on the 21st of August 1808. Later commanders Sir Harry Burrard and Sir Hew Dalrymple halted further attacks and chose to open negotiations instead.
Many people in the United Kingdom viewed the convention as a disgraceful outcome because they felt a complete defeat of Junot had been transformed into a French escape. Critics also noted that Dalrymple ignored concerns about a blockaded Russian squadron in Lisbon which was allowed to sail to Portsmouth despite Britain being at war with them.
An official inquiry began in the Great Hall at the Royal Hospital Chelsea on the 14th of November 1808 and concluded on the 27th of December 1808. All three men were cleared of wrongdoing after the investigation ended, but Burrard and Dalrymple were quietly pushed into retirement while Wellesley soon returned to active duty in Portugal.