No, it's not a plural; it's the simple past subjunctive of "to be", which is "were" for all persons.  See my article from earlier today: https://ell.stackexchange.com/questions/151873/subject-inversion-in-the-correlative-comparative-construction, and my article from November 23rd regarding the subjunctive: https://ell.stackexchange.com/questions/148091/if-you-explained-what-you-trying-to-achieve-i-would/148110#148110.

Here are some examples of the subjunctive although some of them are a bit old-fashioned or archaic or highly formal:

> If **I were** the President of the United States, **I would** cut
> taxes. (both "were" and "would" are simple past subjunctives of "to
> be" and "will" respectively.)
> 
> If **I wanted** you to get involved, **I would** ask for your help.
> (both "wanted" and "would" are simple past subjunctives of "to want"
> and "will" respectively.)
> 
> If **I be elected** President, I shall cut taxes. ("be" is the simple
> present subjunctive of "to be".)
> 
> If **I were elected** President, **I should** cut taxes. ("were" and
> "should" are simple past subjunctives of "to be" and "shall".)
> 
> I shall do it if **he** so **want** me to. ("want" is the simple
> present subjunctive of "to want".)
> 
> It's important that **they be** on their best behavior. (simple
> present subjunctive)
> 
> I demand that **she answer** me! ("answer" is the simple present
> subjunctive of "to answer".)
> 
> O that **she were** mine! (simple past subjunctive)
> 
> If **I had gone** to the party, I **would** have had a great time.
> (past perfect subjunctive of "to go")
> 
> It's imperative that **he have finished** college by the time he is
> 23-years-old. (present perfect subjunctive of "to finish".)
> 
> He talks as though **he knew** everything there is about being in
> love. (simple past subjunctive of "to know".)

The subjunctive is somewhat fancy and formal, but it is still considered good English today; in fact, in some instances, it is considered really good English.  It was more popular during the nineteenth and early twentieth century than it is today, although it's been experiencing somewhat of a revival since it is quite frequently used in American English, particularly the *mandative subjunctive*:

> I recommend that **she not do** that.

It is also very popular in literature, especially literature from the nineteenth century and earlier centuries:

> "Men's courses will foreshadow certain ends, to which, if persevered
> in, they must lead," said Scrooge. "But if **the courses be departed**
> from, the ends will change. Say it is thus with what you show me."
> *Ebenezer Scrooge, A Christmas Carol by Charles Dickens, 19 December 1843.*
> 
> "The basis of our governments [sic] being the opinion of the people,
> the very first object should be to keep that right; and **were it
> left** to me to decide whether we should have a government without
> newspapers, or newspapers without a government, I should not hesitate
> a moment to prefer the latter. But I should mean that every man should
> receive those papers and be capable of reading them." *Letter from
> Thomas Jefferson to Edward Carrington, 16 January 1787, Paris,
> France.*

I hope this might have helped you out.  If you should have any questions, please feel free to ask me.  Take care and good luck!