All of the members of the staff are back at work.

This morning in Starbuck's we were noticing that all of the regular members of the staff at the Starbuck's we usually go to were back. Last week, several of them were on vacation. The temporary staff which was working during the holiday wasn't used to running that branch. They left the garbage bins in the entryway, blocking one of the entrances. That was funny.

Did you notice in the paragraph above that "staff" is treated as a singular noun? That's because it means "a group of employees". Look at these common but incorrect sentences:

• × One staff asked if he could help me.
  
• ○ One staff member asked if he could help me. Someone on staff asked if he could help me.
• × How many staffs are there?
  
• ○ How many staff members are there? How many people are on staff?

Also notice the idiom "on staff" in the sentences above:

• on the staff of 《be ～》～のスタッフ［メンバー・職員］である、入社｛にゅうしゃ｝している、～の幹部の一員である、～に奉職している、～に勤務している ・He is on the staff of our company. : 彼は我が社の社員です。(definition from 英辞郎 on the web)

Some other nouns that represent groups of people include: team, family, band, police. In American English, all of these except "police" should be used without adding "s" to the verb when the noun is singular.

• My team is a big one. It has 30 members.
• I have a big family. There's my three sisters, my dad, my mom, and me. Altogether, that's six family members.
• The police are looking for the criminal, who shot one of their fellow officers.

The grammar police are watching, so be careful. You wouldn't want the other people on staff at your company to find out you'd been ticketed for a "singular noun with plural verb" violation.