“He went to his dentist a good deal.  But what on earth—­”

Antony laughed a third time.

“What luck!” he chuckled.  “But how do you know?”

“We go to the same man; Mark recommended him to me.  Cartwright, in Wimpole Street.”

“Cartwright in Wimpole Street,” repeated Antony thoughtfully. 
“Yes, I can remember that.  Cartwright in Wimpole Street.  Did
Cayley go to him too, by any chance?”

“I expect so.  Oh, yes, I know he did.  But what on earth—­”

“What was Mark’s general health like?  Did he see a doctor much?”

“Hardly at all, I should think.  He did a lot of early morning exercises which were supposed to make him bright and cheerful at breakfast.  They didn’t do that, but they seemed to keep him pretty fit.  Tony, I wish you’d—­”

Antony held up a hand and hushed him into silence.

“One last question,” he said.  “Was Mark fond of swimming?”

“No, he hated it.  I don’t believe he could swim.  Tony, are you mad, or am I?  Or is this a new game?”

Antony squeezed his arm.

“Dear old Bill,” he said.  “It’s a game.  What a game!  And the answer is Cartwright in Wimpole Street.”

They walked in silence for half a mile or so along the road to Waldheim.  Bill tried two or three times to get his friend to talk, but Antony had only grunted in reply.  He was just going to make another attempt, when Antony came to a sudden stop and turned to him anxiously.

“I wonder if you’d do something for me,” he said, looking at him with some doubt.

“What sort of thing?”

“Well, it’s really dashed important.  It’s just the one thing I want now.”

Bill was suddenly enthusiastic again.

“I say, have you really found it all out?”

Antony nodded.

“At least, I’m very nearly there, Bill.  There’s just this one thing I want now.  It means your going back to Stanton.  Well, we haven’t come far; it won’t take you long.  Do you mind?”

“My dear Holmes, I am at your service.”

Antony gave him a smile and was silent for a little, thinking.

“Is there another inn at Stanton—­fairly close to the station?”

“The ’Plough and Horses’—­just at the corner where the road goes up to the station—­is that the one you mean?”

“That would be the one.  I suppose you could do with a drink, couldn’t you?”

“Rather!” said Bill, with a grin.

“Good.  Then have one at the ‘Plough and Horses.’  Have two, if you like, and talk to the landlord, or landlady, or whoever serves you.  I want you to find out if anybody stayed there on Monday night.”

“Robert?” said Bill eagerly.

“I didn’t say Robert,” said Antony, smiling.  “I just want you to find out if they had a visitor who slept there on Monday night.  A stranger.  If so, then any particulars you can get of him, without letting the landlord know that you are interested—­”