"But the thing's impossible!" he said.
Masters turned slowly round and contemplated him. He had the air of a man who, though lost in a strange land, yet hears an old familiar tune.
"Ah," murmured the chief inspector. "Now where have I heard that before? Lummy, where have I heard it before? But look at Sir Henry there! It doesn't seem to bother him any."
H.M. had, indeed, a singularly peaceful air as he lay back in the chair. A fly circled round and settled down on the peak of his hat.
"The case," pursued Masters, "has got to be approached in a different way. It's all crazy and back-to-foremost to start with. We begin by knowing the murderer; but the murderer's the only person who can't be guilty. We—"
"Now, now, son!" urged H.M. soothingly.
But Masters was getting steam up.
"We've got to find someone who exchanged a real dagger for a rubber one, when the evidence proves nobody could have done it. It's no good saying, 'Where were you at such-and-such a time?' We know where they were. It's no good saying, 'How do you explain this bit of suspicious behavior?' Because there isn't any suspicious behavior. There's no behavior at all. Hypnotism! Rubber daggers! Urr!"
He drew his sleeve across his forehead.
"Now, Masters, you're gettin' yourself all hot…!"