The plot involves the investigation of an area of southwest Ireland closed off by an unusual and secretive company that has negotiated a tax arrangement with the Irish Government. Anyone who goes into the area to work does not come out, but unusual advanced products and developments are coming out, along with tax income.
Other countries want to know what is going on, so a suitable patsy is set up to find out what is behind the barrier. The denouement involves aliens who escaped from their dying world, but with only so much advanced knowledge as could be contained in an Earth human mind. You can only pour so much into a limited space.
I read it out of my school library, so pre-1971, but David Duncan's "Occam's Razor" (1957) is not it.