beguiler or duskblade are perfectly functional going straight to 20 without dips or splashes in other classes. (This isn't the only way to play them, they're just classes that work well at each level)

the beguiler handbook is a great overview of the basics on how a beguiler works and good options on how to play one.

your campaign sounds like it will have a lot of roleplay and social stuff in it, so beguiler is probably a great fit. it's one of my favorite classes.

I highly recommend dipping mindbender 1 at 6 for telepathy so you can take mindsight. you won't regret it.

beguiler also has umd, so if there are spells you like that aren't on its spell list, you can supplement it through items.

beguilers are very friendly to new players.

duskblades are as well, but they're more focused on being brutes and inflicting hp damage.