What's the motive?

This week I've got to the end of my rewrite of Snowbird.  And I've had to confront the fact that the original ending didn't work.

At the start of the book I have my heroine Jian aboard a freighter called the Dyami.  She's a starship Coder, and she's been hired to verify another Coder's work.  It's an all-nighter, and she's alone on the ship when she gets an alarm.  Something is wrong in one of the propulsion modules.

What she finds is a skull and bones in one of the power transfer conduits. Which gave me a great end  to the first chapter, and raised some intriguing questions.  How did this person get into the conduit? Who was this person?  And why had they been trying to sneak aboard the Dyami in the middle of the night?

They were all great questions.  The trouble was, I didn't answer them when I came to the end of the novel the first time.  And twenty years ago I didn't have any crime writer friends to call me out on such things.

Now I know better.  I've acquired three crime writer friends, and they've taught me to think about revealing motivations.  They also howl loudly if the psychology of something I've written is implausible.

They've trained me to identify and reveal motive. Of course, I always thought I was writing an SF novel, but there's a fair bit of crime in it too.  Sabotage, crimes of violence, dubious business dealings, murder attempts.  They're all in there.

And at the end of the book I needed to draw these diverse strands together.  Which I didn't do first time round.  How did the attack on Jian's Search team on Angiris link to the presence of that body on the Dyami?

I didn't know.  I hadn't worked the links out,  and I needed to.  Which led me back to the question of motives.  I hadn't worked all of those out either.

There was nothing for it but to grab pen and paper and list out the incidents.  To sit down and work out how and why they link together.  And now that I've done that and know all the motives I can finally give this novel a satisfying ending.