"I care. I guess I just don't mind." - Lindsey, re: his possible death at Darla's fangs in Reunion
That actually reminded me of Eve's attitude at the end of Destiny - she cares about whether or not Spike killed Angel, but she didn't mind that he didn't. And Lindsey's got... it's not a death wish so much as a hurt wish.
They're both flexible when it comes to getting what they what. Neither of them seemed to be terribly attached to any one outcome. It's about moving pieces and seeing what happens.
"What's wrong, Lindsey? Bitter that your girlfriend didn't kill me?"
"More like bummed."
Lindsey's ambigious. Always has been. And he was our introduction to Wolfram and Hart.
Lilah was always more professional than Lindsey. Lindsey gets emotionally involved in projects in a way that Lilah doesn't - even when she cares about Wesley, she never lets it interfere with her work.
So really, when we have an Angel who's letting himself bleed away his emotional contacts and sink into the grey of the work, it makes sense to bring Lindsey back for a wake-up call.
"The road to redeemption is a rocky path."
Even though Angel is instrumental in Lindsey's development, he was never the reason for any of Lindsey's decisions. All of those, from staying with Wolfram and Hart (Blind Date) to finally leaving it (Dead End), all came from Lindsey's own ambiguity.
And it's interesting to note that Lindsey leaves soon after Angel's epiphany and is gone for all of the time that Angel is letting himself forget about the Shanshu. Lindsey is, as others have noted, the person connected most with the Shanshu - once Angel's journey takes him away from thinking about the Shanshu, Lindsey is, for the moment, unneeded.
Really, once the Shanshu was mentioned again, I should have been on the lookout for my boy. The scrolls are introduced in Lindsey's first big episode. He's the one who brings Darla back and who starts the disconnection of Angel from the powers (and now Angel truly is cut off from the PTB - and he hasn't even realized that it was foretold). He told us that "we don't want [Angel] dead. We want him dark." Though he did misunderstand what was meant by that - it wasn't Angelus that W&H wanted - it was a dark Angel.
Lindsey handed the reins over to Lilah (saving her life in the process), but her goals weren't his, and W&H's focus on Angel shifted in the changeover.
Interestingly enough, Lindsey was never really afraid of Angel in the way that Lilah was - he practically challenged Angel to hurt him whenever they met. Again, Eve demonstrates that same lack of fear. Lindsey's been hurt by Angel more often than Lilah has (though Lilah's been threatened more, he didn't hurt her as much) but Lindsey? Well, Lindsey never really seemed to have much of a concern for his own skin after Blind Date - or possibly what happened in To Shanshu in L.A. is what set it up.
Some people have speculated that Eve is a cyborg (if Lindsey is behind the people in Lineage, that would make perfect sense - Roger wasn't detectable as non-human in any way). This actually really tracks for me. And it explains why she has Lindsey's pragmatism and lack of fear of Angel. And why she wears Darla-red clothes. "Sex with robots is more common than people think."
And her ambiguity, again, mirrors Lindsey's.
So, what do we know for certain -
a) they put Sirk in there - which means that they either took advantage of Wes' absence or they arranged it. I suspect that Corporeal Spike is a Plan B. That Lindsey also sent the cyborgs and would have been perfectly happy with a will-less Angel. That's so something Lindsey would think of and it explains why the cyborg knew where to find things in the vault (and also why it needed Wes, after all, I bet Wesley's changed the password and who the vault is coded to).
b) they were kinda hoping that Spike would kill Angel, but were fine with him not - Again, definitely a Lindsey thing. Lindsey, after TSiLA, pretty much never minds the idea that something could lead to Angel's death. He won't force it if a live Angel works with his plans, but he's always willing to change his plans to accommodate a dead Angel.
c) they did it under the Senior Partner's noses - Which means that they are not on the side of Evil. They may or may not be on the side of good - I personally suspect that Lindsey is on the side of himself and people that he likes - which does include the innocent most of the time.
d) this is only the beginning of their plan - Yay! More Lindsey!