Basic rule (plural nouns) When the noun is a normal plural, with an added s, no extra s is added in the possessive; so pens' caps (where there is more than one pen) is correct rather than pens's caps. If the plural is not one that is formed by adding s, an s is added for the possessive, after the apostrophe: children's hats, women's hairdresser, some people's eyes (but compare some peoples' recent emergence into nationhood, where peoples is meant as the plural of the singular people). These principles are universally accepted. A few English nouns have plurals that are not spelled with a final s but end in an /s/ or a /z/ sound: mice (plural of mouse, and for compounds like dormouse, titmouse), dice (when used as the plural of die), pence (a plural of penny, with compounds like sixpence that now tend to be taken as singulars). In the absence of specific exceptional treatment in style guides, the possessives of these plurals are formed by adding an apostrophe and an s in the standard way: seven titmice's tails were found, the dice's last fall was a seven, his few pence's value was not enough to buy bread. These would often be rephrased, where possible: the last fall of the dice was a seven.[5]
thanks to wikipaedia
"gentlemen's" seems ok Eckford, possessive we are talking about,you are correct on the Where's of course.
Scary thing is, I used to know all of this as a kid.
