It is not what Mr. Lorry does but what he decides he must not do: He must not let anyone know about Dr. Manette's condition. Earlier in the day, he had noticed that Manette did not look well, but he didn't make much of it. When Manette goes off to his room, Mr. Lorry decides to let him rest while he visits Tellson. On his return, Mr. Lorry hears a knocking sound. Miss Pross tells him that the doctor doesn't know her and is making shoes. Lorry goes to Manette's room and, seeing his condition, decides he must keep it secret.
Two things at once impressed themselves on Mr. Lorry, as important above all others; the first, that this must be kept secret from Lucie; the second, that it must be kept secret from all who knew him. In conjunction with Miss Pross, he took immediate steps towards the latter precaution, by giving out that the Doctor was not well, and required a few days of complete rest. In aid of the kind deception to be practised on his daughter, Miss Pross was to write, describing his having been called away professionally, and referring to an imaginary letter of two or three hurried lines in his own hand, represented to have been addressed to her by the same post.