The Box With Broken Seals by E. Phillips Oppenheim

That night at dinner time a stranger appeared at the captain's table. A dark, thick-browed man, in morning clothes of professional cut, was shown by one of the saloon stewards to a seat which had hitherto been vacant. Crawshay, whose place was nearly opposite, leaned across at once with an air of interest.

"Good evening, Doctor," he said.