Enter, stage right

[Nonverbis]

Upstream Proficiency by Virginia Evans and Jenny Dooley

Enter, stage right, the prime suspect - work.

As far as I understood a command by a director in a theatre is mimicked here.

The question is why not 'enters'? Is it a mistake, imperative mood or what?

 

[emsr2d2]

It's an imperative. That's how it's used in stage directions too. Imperatives always use the bare infinitive, never the third person singular.

 

[Tdol]

Work is the cause of these postmodern symptoms.