Linearity bores readers. Inexorable drive to a conclusion is good, but readers want twists and turns. And I strongly recommend creating as many hurdles for your hero to overcome as (internally) logically possible.
But take a moment and think about your poor reader, waist-deep in your book, absolutely certain they know where you, the writer, is heading with the story. Clues are being revealed (not too fast, I hope) and a couple may even be red-herrings. And, unless you’re careful, the light at the end of the literary tunnel is visible and an obvious ending is a poor ending.
But a major, earth-moving twist in the middle of your story, well that’ll keep them interested.
After your First Plot Point steer your hero down a path that is essentially right, but not completely correct. Your hero, after all, is spending their time at this stage reacting to the status quo-busting First Plot Point and is in information gathering mode.
And some of that information will lead your hero down a slightly wrong path. Your midpoint scenen should be a “this changes everything” scene. A piece of information unknown to the hero prior to this point aligns the hero on the right path. The complete story isn’t known by the hero yet (it better be known by you, the writer), but the hero is now heading in the right direction.
Or perhaps the midpoint scene reveals to the hero exactly how large the stakes are. Prior to this point, perhaps the hero is looking for an arsonist. Perhaps the midpoint reveals that the unidentified body discovered in the burnt out warehouse has been identified as his long-lost brother.
Subtle or a smack in the face. It doesn’t matter. It just needs to be somewhere in the middle.
Avengers: Age of Ultron. That midpoint is in the garage on Hawkeye’s farm. Tony Stark is asked to look at the tractor that won’t start and when he enters, Sam Jackson’s Fury is waiting. It’s a quiet scene. Hulk isn’t slamming anyone against the wall. Thor isn’t ripping anyone’s head off. Nick Fury is just telling Tony Stark to pull his head out of his ass and sort out Ultron.
Nick Fury: [to Stark] You’ve come up with some pretty impressive things Stark. War isn’t one of them.
The Proposal is a light, fluffy rom-com starring Ryan Reynolds (Andrew) and Sandra Bullock (Margaret). It’s one of those stories where you know out of the gate that they will find themselves together (even though they hate each other at the beginning) and the story is just about how that actually happens.
He works for her, she is a Canadian with an expired visa in the US and she comes up with a plan to “marry” him to stay in the US. They go back to his parent’s place, and are growing more and more in hate when there’s a meet (meat) cute after they both have a shower. They run into each other, naked and she lands on top of him. Feelings ensue.
In the scene immediately after this one they start sharing intimate details of their life. The nudie scene changed everything.
Bottom line, use the midpoint scene to alter the hero’s target. Shake things up. And advance the story in the right direction while you’re at it.