Vinewood Souvenirs - The Last Act is a Strangers and Freaks mission for Trevor. This is the last outing with Nigel and Mrs. Thornhill.

The celebrity you helped kidnap needs to be taken care of. Bring him to the railroad tracks and park your car on the tracks. The train will later hit the car, killing the celebrity, and the mission will after Trevor calls Nigel to inform him of what happened.

For the gold completion, drive towards the train and jump out of the car when prompted. (getting out when the car was not moving didn't work for me)

Alternitively, you can save him by pulling over when prompted and earn around $3000 in the process. However, this means you can't get the gold completion. Later on he will offer you $10000 when you should be reaching the railroad.