The one good thing about DC's brief licensing of "The Avenger" was that it eventuated in this crossover. Certainly the story was an attempt to boost the visibility of the lesser-known feature, but the raconteurs in charge of having the Shadow and the Avenger-- Uslan and Cruz-- also made it one of the stronger comics-crossovers of the 1970s.
I won't claim that the plot is anything special. Both heroes employed crews of subsidiary agents who helped the main guy fight his battles, so the script took advantage of this by having a nasty evildoer-- the Shadow's most celebrated villain, Shiwan Khan-- kidnap members from both crews. He then hypnotized the assistants and used them as catspaws in a successful attempt to make the two crime-crusaders fight one another.
As a fight, it's not much: ER Cruz is more successful at creating oppressive mood than pulse-pounding action. But Uslan is excellent in the way he gives both the Shadow and the Avenger a waspish wariness of one another, rather than simply having them make nice once they learn how they've been manipulated. I particularly like the succinct way the Avenger explains things to a subordinate when they witness one of the Shadow's quasi-supernatural feats: ""All is not as we see it, Mac! But I DO know what it was I saw!" At a time when many comics-writers over-explained nearly everything in the story, Uslan shows a charming reticence as to divulging the inner secrets of his mysterioso protagonists.