On 12 July 1418, Thomas Corbet, gentleman of London, was in the Marshalsea prison, incarcerated there to force him to answer to a trespass suit launched by one Matthew Preston.
A Lombard named Alexander Jon (Alessandro Gianni?) “fraudulently machinated” so that Corbet was able to escape from the Marshalsea and flee to sanctuary at Westminster. If Corbet is the man of the same name mentioned in the patent rolls in following years, he seems to have extricated himself from this situation and went on to prosperity; it was the deputy in charge of the Marshalsea who got into trouble.
TNA, KB 9/211, m. 10; CPR 1416-22, 238, 336, 368. Image https://www.dkfindout.com/us/history/castles/castles-as-prisons/