The inflection to –s, –es or –ies to indicate plurality may seem at first sight to be a straightforward matter, but any serious writer or editor should pay attention to the following.
 

• detail
  Despite its countable status, its singular form is used in phrases such as in detail and go into detail.

• talent
  It is countable when it refers to a person’s special skill or natural gift, but if referred to people with such skill or gift, no –s is required. Thus,
  The competition has attracted talent from all over the country, and those who made it to the final flaunted their talents in a show televised to millions.

• offspring
  Some words, like the above example, never inflect even when used in a plural sense. Thus, a great man can never have mediocre offsprings.

• grounds, commons, bounds
  When referring to a place or territory, all the above words cannot rid themselves of a sibilant ending. Examples are: school grounds, learning commons, out of bounds.

• compound nouns
  Lastly, the plural inflection does not necessarily occur in the last word of a compound noun, e.g., sons in law, ladies in waiting, masters of ceremony, deans of students.

Editor
www.iso.cuhk.edu.hk/english/features/style-speaks/index.html