Fate/stay night, Vol. 6

Shiro activates his command mantra, summoning Saber to his side, while Rin and Archer attack Shinji and Rider, pushing them to the edge of defeat.  But Saber blocks Archer's final blow - under Shiro's orders - promising to defend Shinji even at the cost of breaking their agreement with Rin.  But can they convince Shinji to cease his immoral acts? And Rider questions Saber's loyalty to a Master who doesn't even want to fight - just what are Saber's true reasons for obeying Shiro?