Silver Streak (1976)

Aboard the rapid Silver Streak train, recently-divorced Los Angeles non-fiction book publisher George Caldwell is on his way to Chicago to attend his sister's wedding. Eager to spend two carefree days of sluggish monotony, the bright-eyed bachelor instead strikes up an acquaintance with beautiful, blue-eyed fellow passenger Hilly Burns, and suddenly life is exciting again. Then, out of the blue, George catches a glimpse of a murdered man outside his window, and although nobody believes him, the unsuspecting traveler becomes entangled in a dangerous conspiracy. Before long, bullets start flying, and George is soon framed for murder. And... is there more to lovely Hilly than meets the eye? Above all, can Caldwell get to the bottom of this intricate mystery and clear his name?