Research done: Google search on Flunitrazepam, corresponding Wikipedia entry (via Google search on "knockout drug," "mickey finn," et cetera), a few entries in this community on this and related topics
My story involves a scene where two characters, a novice spy (who's stumbled into something well beyond his training at this point) and his much more experienced partner, are having dinner at a nice restaurant attached to their hotel. My ideal situation is this: they order a bottle of wine and the novice drinks first, but the wine has been drugged and after a little while he either blacks out completely, or becomes very uninhibited and has no memory of the occasion. His partner has not had any wine by the time that the novice exhibits symptoms, and is able (with help) to get him to their room and wait for him to wake up. Novice regains consciousness after an appropriate amount of time (I can work with just about any time window here, but six to ten hours is what I've been envisioning), with a terrible headache and light-sensitivity. Either way, partner turns the lights off for a while as novice recuperates. My drug of choice for this debacle is Rohypnol/Flunitrazepam, since as far as I can tell, it covers the necessary bases (though if there's a substance that would take effect faster, I am open to that), and assume the person responsible for drugging them knows the correct dosage to get the effect he wants (i.e. incapacitate the two men and capture/interrogate them).
My research so far suggests that Flunitrazepam takes about twenty minutes to start affecting someone when taken orally, and that alcohol can intensify its effects. Would alcohol cause it to work faster, or just make its effects stronger? How soon would a trained observer know that something was wrong? Would the drugged person feel or taste anything right away that he could remark upon, thus alerting his partner, even if it's just an odd taste or texture to the drink?
Would the drugged person pass out very quickly (i.e. twenty minutes pass, and then, bam, he's on the floor), or would he slowly get sleepier/less coordinated over a longer period of time? Same question with the amnesiac effects - at what point would the gap in his memory begin?
One site that I checked said that it may have a bitter taste when mixed with alcohol, but would this be noticeable in something like wine that is already pretty strong? It seems like Flunitrazepam comes in tablets, so would these be crushed and dissolved in the liquid, or is there also a liquid form?
As for side-effects/after-effects, I've read about headaches and digestive upset, so how long would they last after waking up, and how intense are they?
That's an awful lot of questions, so... many, many thanks in advance!