"Two Mules for Sister Sara" unfolds with Hogan (Clint Eastwood of "Hang'em High") is riding one horse and leading another loaded with supplies though the dangerous Mexican wilderness. The leisurely title sequence features a variety of critters starting with a hoot owl, followed by a fish gliding through a stream, a cougar poised and panting on a rock ledge, a snake slithering across the sand, and concludes with Hogan's horse crushing a tarantula under its shod horn. Our protagonist is minding his own business when he stumbles accidentally onto three drunken guys and a naked woman in the middle of nowhere. The gunmen offer to share the lady, but then treacherously try to kill our hero over her. Hogan guns two of them down with relative ease, while the third seizes the woman and uses her as a shield. Hogan ignites a stick of TNT and slings it at them. The third man fires at Hogan and flees in desperation to avoid getting blown to bites. Hogan drops him with three shots in the back. He descends the slope, snuffs out the burning fuse on the stick of dynamite, and suggests that the naked lady put on her clothes unless she wants to be sunburnt to hell and gone. Afterward, Hogan discovers the naked lady is in reality a Catholic nun! He helps her bury them and then blows his cool when he sees Sara sprinkling his canteen on their graves. He snatches his canteen and suggests that she bless them without water since they are in the middle of an arid region. Things turn even weirder when a column of French cavalry show up and Sara goes berserk. She cannot let the French capture her, she explains rapidly to Hogan, because she is working in league with the revolutionaries. Hogan unearths the dead killers and sends them off at a gallop on the backs of their ponies for the French to pursue. Hogan and Sara slip away.
Hogan has come to Mexico to help destroy a French prison on Bastille Day, and he winds up escorting Sara to the prison town. Before he reaches the prison, Hogan gets really drunk after the Yaquis shoot an arrow into his shoulder. Sister Sara uses the reflection off her cross to drive the superstitious Indians away. The scene where she has to remove the arrow from Hogan's shoulder is pretty gritty stuff. Hogan gets himself lickered up to tolerate the pain while Sara digs around the shaft of the arrow and carves a groove in it so he can put gunpowder on it, fire it up, and push it out the back of his shoulder. This scene can be rough on the squeamish. Anyway, since he is tanked enough up to withstand the pain of the arrow removal, Hogan has a difficult time with a train that he is supposed to destroy. He cannot climb the trestle to lash sticks of TNT to the pylons so he convinces Sara--who has a fear of heights--to climb up it and attach the explosives. It is ironic that a nun would hate to ascend and this plays into the big revelation at fade-out. Here comes the train and Hogan misses every shot until Sara hauls off and decks him. He recovers and nails one stick of dynamite and the entire structure collapses under the train.
The big finale finds Hogan and Sara along with some revolutionaries staging an attack on a French fortress. Siegel turns this scene into a massive combat sequence with Hogan demonstrating that he is an excellent shot with either hand. There are a couple of bloody shots in this battle sequence. A guy gets a machete in the head is an example. As usual, Clint is a cool as a cucumber. The big surprise--which I won't reveal--concerns the way that Hogan's relationship with Sara concludes. "Two Mules for Sister Sara" is part shoot'em western and part romance and together a very amusing adventure opus.