A possible Derrick and Zach alliance makes me fearful for the other players.
There's nothing "possible" about it. They've been aligned (along with Cody) as part of the Jump Street alliance since early on.
The only variable is that Zach has put more value into his 2-man alliance with Frankie.
Frankie has (to some extent) outed Jump Street to Christine (his preferred Final 2 partner). And Cody is part of that group as well.
That 5-some is kind of interesting because there are essentially multiple layers to it.
Frankie+Zach
Frankie+Christine
Frankie+Christine+Cody
Zach+Cody+Derrick
Derrick has the least amount of loyalty within that group but he has the best social game outside of it.
And, of course, there's some spillover on the Frankie+Christine end of things involving Caleb, Hayden and Nicole with overlapping layers as well.
The important takeaway is that the Bomb Squad is officially done for most of these people and they have zero loyalty to Devin or Amber.
Frankie's likely going to be the one to light the fuse but he wants to do it in a way that allows him to keep Caleb in his corner after the explosion.
(Cody may light that fuse as well if it means he can save Brittany from getting evicted next week.)