This will probably run contrary to all the other advice you get here, but my take is: it doesn't matter whether they have a stock plan yet. It is not as if a pre-existing stock plan really protects you; after multiple rounds of VC, any deal that was on the table when you started will have been rewritten many times over.
Though an option plan doesn't protect you, once you've been granted a specific number of options (or rather, restricted stock), there is little anyone can do do take them away from you, short of firing you, without diluting the founders equally.
That depends on your class of equity! Your terms might be different to the founders - in the UK you can read the memorandum and articles to understand the current equity structure and dilution rules for a company.
(Changing the mem and arts usually requires a shareholder meeting, and can be contested in court if the interests of minority stock holders are not taken sufficiently into consideration.)
In addition even if you do hold stock of the same class as the founders that won't always prevent you getting screwed over. The board might sign up to a sucky deal through innocence, incompetence or collusion and condemn you as a side effect.
This is kind of along the lines of what the senior people at the company were telling me. That you have to believe in the idea of the company and have faith that they will take care of employees and want you to be 110% committed to making the company a huge success by giving you a generous equity package.
Don't fall for that. If the company wants to see if you are a good fit before hiring you they should hire you as a contractor and pay a good hourly rate. Which from my experience in the Bay Area is at least 75 bucks an hour for 40 hours a week.
This "try before you buy" contractor meme is awful. 1099s are responsible for their own payroll taxes and their own health insurance. If a company suggested that I relocate for the opportunity to consult with them, I'd hang up the phone. It's insulting.
(Obviously, I mean, as a half-measure before extending a full-time offer. If a company suggested that Matasano consult for them, we'd thank them and then make it happen.)
The consultant/contractor would likely be to avoid payroll taxes/withholding/processing fees with TriNet etc - not to avoid giving equity. (And, technically, it's illegal to "pretend" someone is a contractor when they're not - but that's a separate issue :)
Remember, this is all at-will employment - either of you can end the relationship at any time. This is where an equity grant/option with cliff vesting comes in. 4 yrs with a 1yr cliff is fairly standard... In other words, if you get fired or leave before 1 yr, you don't get that equity/option and it reverts to the company.
