Your team is being sent to Black Mesa, a top secret research facility, to provide enhanced security for some high risk tests. The management are worried that something serious will go wrong so you will be on hand to protect the scientists and civilians in the facility.
Board the transport train to gain access. Do not attempt to leave the train while it is in transit, you will die. Once inside report to security to get clearance to go inside the facility.
Sit back and enjoy the ride.