Prehistory of the Serious Sam addon

So, a few words about the campaign and it's development.
 In the beginning of creating levels I hadn't main plot of the campaign. Time was running... the first level was almost done... then second. And only then I seriously thought about  the plot. And when I thought, everything (to my surprise) stepped in logical sequence. And because of that I called my campaign "The prehistory of Serious Sam" (truly there nothing is said about how Nectrisa was implanted in Sam).
This campaign was created for my mod "CRAZY Serious Sam 3: BFE Mod", but most likely, someone will want to play it without the mod. That's why, I just posted this campaign.