Career of Evil
If anyone hasn't watched Career of Evil yet, do yourself a favor and read the book first. The book is amazing, and I'm saying that after I had already seen the TV adaptation of it. I can't imagine the ride it would've been if I went into the book blind to anything about it. Wow.
Every single thing is personal for Strike (and Robin) in Career of Evil. The conflict both professionally and personally is tense. His attraction and feelings for Robin are blossoming and reaching his conscious mind. Robin is being pulled toward Strike as well. Every event and every character adds up to a superb read.
I don't think it's necessary to read The Cuckoo's Calling and The Silkworm to dive into Career of Evil. They were good, with The Silkworm being better than The Cuckoo's Calling, but they really just get everyone and everything in motion. Career of Evil is enhanced because we get more Robin than the first two books.
I'm still perplexed at how the series just barely scratches the surface of what happens in the books to the detriment of understanding the mystery. All the scenes that made me furiously flip pages were not put in the series. Too much is left to inference which would be impossible to figure out unless one reads the books.