The first approach to a solution of the problem which I obtained came a week or two later.  Sebastian was engaged in observing a case where certain unusual symptoms had suddenly supervened.  It was a case of some obscure affection of the heart.  I will not trouble you here with the particular details.  We all suspected a tendency to aneurism.  Hilda Wade was in attendance, as she always was on Sebastian’s observation cases.  We crowded round, watching.  The Professor himself leaned over the cot with some medicine for external application in a basin.  He gave it to Hilda to hold.  I noticed that as she held it her fingers trembled, and that her eyes were fixed harder than ever upon Sebastian.  He turned round to his students.  “Now this,” he began, in a very unconcerned voice, as if the patient were a toad, “is a most unwonted turn for the disease to take.  It occurs very seldom.  In point of fact, I have only observed the symptom once before; and then it was fatal.  The patient in that instance”—­he paused dramatically—­“was the notorious poisoner, Dr. Yorke-Bannerman.”

As he uttered the words, Hilda Wade’s hands trembled more than ever, and with a little scream she let the basin fall, breaking it into fragments.

Sebastian’s keen eyes had transfixed her in a second.  “How did you manage to do that?” he asked, with quiet sarcasm, but in a tone full of meaning.

“The basin was heavy,” Hilda faltered.  “My hands were trembling—­ and it somehow slipped through them.  I am not . . . quite myself . . . not quite well this afternoon.  I ought not to have attempted it.”

The Professor’s deep-set eyes peered out like gleaming lights from beneath their overhanging brows.  “No; you ought not to have attempted it,” he answered, withering her with a glance.  “You might have let the thing fall on the patient and killed him.  As it is, can’t you see you have agitated him with the flurry?  Don’t stand there holding your breath, woman:  repair your mischief.  Get a cloth and wipe it up, and give me the bottle.”

With skilful haste he administered a little sal volatile and nux vomica to the swooning patient; while Hilda set about remedying the damage.  “That’s better,” Sebastian said, in a mollified tone, when she had brought another basin.  There was a singular note of cloaked triumph in his voice.  “Now, we’ll begin again. . . .  I was just saying, gentlemen, before this accident, that I had seen only one case of this peculiar form of the tendency before; and that case was the notorious”—­he kept his glittering eyes fixed harder on Hilda than ever—­“the notorious Dr. Yorke-Bannerman.”

I was watching Hilda, too.  At the words, she trembled violently all over once more, but with an effort restrained herself.  Their looks met in a searching glance.  Hilda’s air was proud and fearless:  in Sebastian’s, I fancied I detected, after a second, just a tinge of wavering.