The Newton family from the first two Beethoven movies is on vacation in Europe, but they do plan to attend a Newton family reunion, and to make sure one of their family members definitely makes it, they ship him to travel to there with George's brother, Richard.
Guess which one it was? That's right, Beethoven.
He follows Richard and his family as they hit the road to California in a huge, shiny, and expensive RV, equipped with a DVD player.
Following them are two bumbling crooks who have hidden some secret codes on a DVD that they figure no one in the world will buy, but someone does: Richard.
So now they have a DVD holding top secret information, and the crooks must get it back.