The Box With Broken Seals by E. Phillips Oppenheim

Katharine came on deck that morning in a somewhat disturbed frame of mind. It was beginning to dawn upon her that her position as sick nurse to Mr. Phillips was meant to be a sinecure. She was allowed to sit by the sick man's side sometimes whilst the doctor took a promenade or ate a meal in the saloon, but apart from that, the usual exercise of her duties was not required from her. She was forced to admit that there was something mysterious about the little stateroom, the suffering man, and the doctor who watched him speechlessly night and day.

She was conscious presently that Crawshay, who had been walking up and down the deck, had stopped before the chair on which she lay extended. She greeted him without enthusiasm.