Fury

Hmm - this one was extremely creaky.

The protagonist, an unlikable, Campbellian "Competent Man" engages in a see-saw battle of wits and derring-do with the leaders of humanity, the Immortals (themselves a fairly unlikable bunch). Somehow, the fate of humanity was at stake (but it mostly just seemed like the protagonist was trying to save his own skin, and to bloody the other guy's nose), and things were oh so dramatic (I could tell by the liberal use of italics and exclamation marks), but mostly it was just a struggle (and I suppose it didn't help that I picked this up not knowing that it was the second book in a duology).

I don't think I'm much of a fan of Kuttner (I also didn't much like his Best of collection, read many years ago), but then there were the Padgett (a pseudonym for Kuttner & Moore) stories (The Twonky, Mimsy Were the Borogoves, etc.), for which I have fond memories. It's complicated by the fact that Kuttner was rarely writing entirely alone - his wife, C. L. Moore, generally regarded as the superior writer of the two, often had a hand in Kuttner's work. She definitely provided some assistance in Fury, but the enjoyable Padgett stories were apparently more of a 50/50 collaboration