Captain...
[
She's gone. She's gone without a trace and Holmes knows this because he's been keeping an eye on her room and the subtle changes around it, which is on deck six, a bit of a stroll - on the absolute opposite corner of the boat from his - but good exercise nonetheless. Easier to stay unseen, depending on how he approached the walk.]
[Sherlock had been quietly observing her (by all current accounts, seemingly mild and unsuspicious) methods, waiting for Irene to make a move in conformity with her indefinitely free spirit; and found that, when she finally did, he was entirely unprepared for it. Did she figure out something he didn't? Was there some practicality to the comings and goings of this place that he'd missed?]
[This fits in perfectly with the other disappearances that have been previously mentioned to him; the case presented to him by Bryn that he hadn't the experience to tackle just yet, the proficiency with the time. He's reluctant to believe that Irene is really a victim of it, the word "victim" in conjunction with "Irene" an alien sort of concept, and opted instead to persue the dead-end avenues first for something overlooked - something else plausible, but therein lies his bias.]
[And so, completely boggled (for now) by this new development, he continues to build Irene up in his mind as a most formidable challenge opponent.]
[In other news, not being pushed to do manual labour or pay rent - or pay for anything - has put the Captain in a favourable standing in Holmes' mind.]
...I think you may have an overlooked security issue.