FWIW I found Essentials of Plastic Surgery by Janis was very beneficial during my Sub-I's, it helped on a lot of the basic questions I got during my rotations, plus it was a great read in between cases when there would be a last minute schedule change and I was in a different case than I prepared for. It doesn't give a great background on each topic but probably more than enough for a 4th year medical student.
If you are intent on reading from a large text, I think you would be better off targeting the most common cases you will see (Breast Reconstruction/Reductions, facial trauma, Hand, basic flaps), rather than trying to get through a whole book, because while reading the Grabb and Smith chapter on facial reanimation is interesting, it probably won't be the most productive use of your time to maximize your pre-rotation reading, since you may not be involved with those cases during your rotation.
For every case I scrubbed in, anatomy was by far the most common questions I was asked, so reviewing hand and facial anatomy before your rotation would make life easier for you when you start your rotations. I would also find out as much as you can about the institution you are rotating at, if they are very heavy in one area of plastic surgery (breast/hand/craniofacial), then target your reading toward that.
With all that said, stuff you read 4 months ago probably won't help you during your day to day interactions with faculty, because you are less likely to remember those key "pimp" questions but I think having a basic understanding of what is going on will make you more useful during the case, which ingratiates you with the residents and makes them more likely to vouch for you when the faculty asks about your performance.
