Complex sentence: As a newbie prank, the other rousties make him clean-up a baggage trailer, where Ben finds a photograph of his mother, but when he shows it to Samson, he is told that there never was a baggage trailer.
Split into simpler sentences: As a newbie prank, the other rousties make him clean-up a baggage trailer, where Ben finds a photograph of his mother. He shows it to Samson, who explains that there never was a baggage trailer.