With a peremptory wave of his hand Kennedy silenced the Jap.
"It has long been a question," he hurried on, "whether these vitamines are tangible bodies or just special arrangements of molecules. Recently government investigators have discovered that they are bodies that can be isolated by a special process from the filtrate of brewer's yeast by Lloyd's reagent. Five grams of this"—he held up some of the tablets he had made—"for a sixty-kilogram person each day are sufficient. Unknown to you, I have introduced some of this substance into the food already deficient in vitamines. I fancy that even now I can detect a change," he nodded toward Mrs. Wardlaw.
There was a murmur of surprise in the room, but before Craig could continue further the door opened and Mrs. Wardlaw uttered a nervous exclamation. There stood Chase with a woman. I recognized her immediately from Kennedy's description as Miss Hackstaff.
Chase walked deliberately over to Kennedy and handed him something, while the nurse glanced calmly, almost with pity, at Mrs. Wardlaw, ignoring Wardlaw, then fixing her gaze venomously on Miss Langdale. Recalling the incident of the morning, I was ready to prevent, if necessary, a repetition now. Neither moved. But it was a thrilling, if silent, drama as the two women glared at each other.
Kennedy was hastily comparing the anonymous note he had received with something Chase had brought.
"Some one," he shot out, suddenly, looking up and facing us, "has, as I have intimated, been removing or destroying the vital principle in the food—these vitamines. Clearly the purpose was to make this case look like an epidemic of beriberi, polyneuritis. That part has been clear to me for some time. It has been the source of this devilish plot which has been obscure. Just a moment, Kato, I will do the talking. My detective, Chase, has been doing some shadowing for me, as well as some turning over of past history. He has found a woman, a nurse, more than a nurse, a secret lover, cast off in favor of another. Miss Hackstaff—you wrote that letter—it is your hand—for revenge—on Miss Langdale and—"
"You shan't have him!" almost hissed Helen Hackstaff. "If I cannot—no one shall!"
Natalie Langdale faced her, defiant. "You are a jealous, suspicious person," she cried. "Doctor Aitken knows—"
"One moment," interrupted Craig. "Mrs. Marbury is gone. Mrs. Wardlaw is weakened. Yet all who are affected with nerve troubles are not necessarily suffering from polyneuritis. Some one here has been dilettanting with death. It is of no use," he thundered, turning suddenly on a cowering figure. "You stood to win most, with the money and your unholy love. But Miss Hackstaff, cast off, has proved your Nemesis. Your nervousness is the nervousness not of polyneuritis, but of guilt, Doctor Wardlaw!"