Meanwhile they had all pressed forward to the window.  Frederick, who carefully kept his face out of his father’s view, bent half-way over the sill in his anxiety to watch the flying figure of Sweetwater, who was making straight for the dock, while Knapp, roused at last, leaned over his shoulder and pointed to the sailors on the deck, who were pulling in the last ropes, preparatory to sailing.

“He’s too late:  they won’t let him aboard now.  What a fool to hang around here till he saw his man, instead of being at the dock to nab him!  That comes of trusting a country bumpkin.  I knew he’d fail us at the pinch.  They lack training, these would-be detectives.  See, now!  He’s run up against the mate, and the mate pushes him back.  His cake is all dough, unless he’s got a warrant.  Has he a warrant, Dr. Talbot?”

“No,” said the coroner, “he didn’t ask for one.  He didn’t even tell me whom he wanted.  Can it be one of those two passengers you see on the forward deck, there?”

It might well be.  Even from a distance these two men presented a sinister appearance that made them quite marked figures among the crowd of hurrying sailors and belated passengers.

“One of them is peering over the rail with a very evident air of anxiety.  His eye is on Sweetwater, who is dancing with impatience.  See, he is gesticulating like a monkey, and—­By the powers, they are going to let him go aboard!”

Mr. Sutherland, who had been leaning heavily against the window-jamb in the agitation of doubt and suspense which Sweetwater’s unaccountable conduct had evoked, here crossed to the other side and stole a determined look at Frederick.  Was his son personally interested in this attempt of the amateur detective?  Did he know whom Sweetwater sought, and was he suffering as much or more than himself from the uncertainty and fearful possibilities of the moment?  He thought he knew Frederick’s face, and that he read dread there, but Frederick had changed so completely since the commission of this crime that even his father could no longer be sure of the correct meaning either of his words or expression.

The torture of the moment continued.

“He climbs like a squirrel,” remarked Dr. Talbot, with a touch of enthusiasm.  “Look at him now—­he’s on the quarterdeck and will be down in the cabins before you can say Jack Robinson.  I warrant they have told him to hurry.  Captain Dunlap isn’t the man to wait five minutes after the ropes are pulled in.”

“Those two men have shrunk away behind some mast or other,” cried Knapp.  “They are the fellows he’s after.  But what can they have to do with the murder?  Have you ever seen them here about town, Dr. Talbot?”

“Not that I remember; they have a foreign air about them.  Look like South Americans.”

“Well, they’re going to South America.  Sweetwater can’t stop them.  He has barely time to get off the ship himself.  There goes the last rope!  Have they forgotten him?  They’re drawing up the ladder.”