Rubin and Mullin get points for not making this a traditional buddy movie, but their decision to take the plot down an unexpected road -- and never getting back to the pure feeling of friendship that drives the first half -- leaves Semper Fi lacking.

The interesting characters and all of their conflicts are all right there onscreen -- the cast is excellent -- but the 'prison break' is such a far-fetched idea it's difficult to invest in it.

Both halves are handled well by director Henry Alex Rubin, who also co-wrote the film with U.S. Army vet Sean Mullin. But whenever the film shifts its focus to one side of its story, the other suffers.

An unpersuasive action-driven movie rather different to the steady character fare that previously held our attention.