Your name is Gordan Freeman.  You have a Ph. D. in theoretical physics from  MIT.  You are well acquainted with classical physics, relativity and  quantum mechanics.  You presently work at a top-secret research compound in  New Mexico called the Black Mesa Research Lab.  However, this is not going  to be just another typical day at the office.  It will be a period that  will test you in ways that your education at MIT did not prepare you  for...