In my view, you've made a whole bunch of mistakes. The important things to do are to recognise the mistakes so you don't make them again, and decide on a course of actions going forward.
ptolemy18 said:
Firstly, I'm running a game with no alignments, because it's a pseudo-historical game (Ancient Egypt) and I wanted the relations between different countries & factions to be fairly cutthroat.
There's nothing in the alignment system to preclude this. Still, if you want to ditch alignment, that's fair enough.
ptolemy18 said:
Anyway.... one of the PCs recently was retired by the player, who introduced a new PC to take their place. The old PC was a basically good cleric; the new PC is a cleric of a different religion, who worships Ahura-Mazda, Supreme God of Good. I've told the player that, although there is no alignment system, I will give him certain abilities (the ability to spontaneously cast spells of either of his cleric domains) as long as he roleplays the character in a suitably pseudo-lawful-good fashion.
Right. First two mistakes.
1) If you're ditching alignment, then ditch alignment. Don't ditch alignment, and then talk the player into behaving according to the LG alignment. (What you should have done is defined a suitable code of conduct for each of the gods, effectively replacing the alignment restrictions for Clerics. In fact, you should do this whether you use alignment or not - none of the alignments are so monolithic as to fully define a religion.)
2) Don't give out game-mechanical bonuses for role-playing 'penalties'. Either the PC will do what he's going to do anyway, and get something for nothing, or at some point you'll have to take away the benefit, and deal with complaints from the player.
ptolemy18 said:
The old PC and the new PC meet up for about two hours' time, in-character. The old PC, who is retiring, gives the new PC (who she has never met before) her magic items since she is 'retiring from adventuring'. :/ Since the new PC is taking the old PC's place as the party cleric, this is borderline acceptable, I guess. (Although maybe this is where I made my mistake...)
Yep, mistake 3. As soon as the new PC is on the scene, the old PC is retired, and is therefore an NPC. This prevents the issue even arising.
ptolemy18 said:
Later the same night, however, the old PC (still being player intermittently by the player) goes off to talk to some government officials to plead for mercy in the case of an NPC who has been accused of treason. Instead of being friendly, the officials cast "Zone of Truth" on her, find out that she was involved with a fight with some government troops a few sessions ago, and throw her in prison. End of the old PC.
Neat trick. Sadly, creatures affected by Zone of Truth are aware of the effect, and are not compelled to answer questions - only to speak the truth if they speak at all. So, this is unlikely. Still, it does get rid of the PC.
ptolemy18 said:
Except that, the rest of the party knows she's been imprisoned. They go to the city a few days later, and see their old former-PC friend chained up in the marketplace, being deprived of food and water until she agrees to give the names of other rebels (i.e. the player characters). (And if she dies of starvation and dehydration, the government will use "Speak with Dead" on her to find out the info anyway.)
Again, Speak with Dead allows a save, and since Will saves are good for Clerics, this is likely to not work.
ptolemy18 said:
The party goes to the former-PC's temple to ask them for help, and all the priests are outraged to find out what happened, but they worship a pacifistic god, and the high priestess tells them that they can't directly confront the government; instead they'll just have to try to plead for mercy on the former-PC's part.
Now, at this point, I expected the party to get in a debate: should they try to help/rescue the former PC, or should they not bother? I was really prepared for either way. What surprised & irritated me as DM was that the player who used to play the imprisoned PC, who's now playing the Priestess of the Supreme God of Good, *didn't* want to rescue the old PC. :/
More fool them. At some point, their friend will implicate them, and they get to enjoy the 'justice' of their kingdom.
From a good-play point of view, the PCs should have gone to rescue their friend, and co-conspirator. At the worst, they should have gone to make sure he couldn't inform on them. Either way, they really should have acted. The only one who can be excused, in fact, is the new PC, but even in his case, there are two good reasons he should have acted.
However, and this is the important point,
it's the player's choice.
ptolemy18 said:
Now, since there are no alignments, I can't *force* or railroad the players into having their characters act a certain way.
This is your most spectacular mistake. Alignments or no, the DM never has the right to "force" a PC to take a particular action (exception: domination-magic). You get to control everything else about the world - the players have free reign over their PCs.
Now, the key question is where you go from here. I recommend the following:
1) Write up proper codes of behaviour for the deities in your setting. These don't have to be long, but they should be sufficient for your task. One of the key benefits of not using alignments is that you should feel freer to build complex moral codes - a deity might institute all manner of codes of justice as they relate to one group, but then advocate that their followers commit all manner of atrocities against outsiders, for example. This is possible using alignments, but it is easier without. This solves your problem with pseudo-alignments.
2) Take the ex-PC out of the campaign as soon as possible. It doesn't really matter how you do it, but get rid of him. Kill him off, have him rescued by others, have the PCs rescue him and then have him ride off into the sunset, whatever. The sooner he's gone, the better for your campaign.
3) Don't do anything to take back the magic items from the PCs. You shouldn't have let them get them, but what's done is done. For a while, cut back on the treasure the PCs get, until they're back at the 'right' level.
And that's about it. Forget about this situation and move on. Your campaign will benefit from it.