A client.
How the dialogue actually went in the canon:
“Very sorry to knock you up, Watson,” said he, “but it’s the common lot this morning. Mrs. Hudson has been knocked up, she retorted upon me, and I on you.”
“What is it, then–a fire?”“No; a client. It seems that a young lady has arrived in a considerable state of excitement, who insists upon seeing me. She is waiting now in the sitting-room. Now, when young ladies wander about the metropolis at this hour of the morning, and knock sleepy people up out of their beds, I presume that it is something very pressing which they have to communicate.”
