"The Cat Who Walked through Walls" by Robert Heinlein...

Now Heinlein is usually kind of obnoxiously sexist so having a book that opens with what appears to be an actual female character with not just more personality than a playboy magazine centerfold, but what seems like big dick energy action heroesque swagger felt FRESH. Strong start as you get this hyper competent husband and wife team quiping their way through adventures in the backwoods hillbilly country of Earth's moon with their pet bonsai tree to stop a nefarious plot with some promised dimensional McGuffin.

Book stalls out in the middle as they end up in like... A swinger commune. They introduce a huge number of characters all at once alongside this whole poly romantic political dynamic and start mulling over the planning stage of what seems like a complicated heist plot. Feels a lot like a sex party version of the Council of Elrond with each of these characters having complex individual dramas they are in the middle of resolving...

Aaaand smash cut. None of those characters mattered. We are with the protagonist, the heist plan failed spectacularly off stage and we are now in his final dying moments where we realized that cool wife / super spy set him up to fail like a chump at this very moment for... reasons? I dunno, Bitches amirite?

First time I ever finished a book and threw it angrily into the nearest wall.