Nicholas Skeres was part of a group, also including Ingram Frizer and Robert Poley, that were hired to kill Christopher Marlowe. Nicholas was the one assigned to do the job. He had no trouble with thieving, but balked at murder. The other two men threatened him at knife point, and he agreed to do the job.
He found Marlowe in a pub, and stabbed him. He did not know that "Marlowe" was actually the Fourth Doctor, and that the Doctor had been protected from the knife by a copy of Shakespeare's works in his breast pocket. (PROSE: All Done with Mirrors)