Hiding Alignment and Activities
Only in the most restrictive societies will there be prohibitions against merely possessing an alignment. After all, being evil doesn't necessarily mean acting evil all the time, and evil creatures can contribute to a group's--and a society's--prosperity just as other creatures can. Evil can still have friends.
This means if the character's friends discover his alignment, it shouldn't be a big deal. Unless the character's friends are in the habit of killing what they perceive as evil in all its forms (e.g. unkind shopkeepers, misbehaving children, feral cats), a fellow adventurer's alignment shouldn't matter except to those with codes prohibiting association, especially if the other characters have fought beside or had their lives saved by the newly-revealed evil character. But, if the character must keep his alignment secret from a city full of paladins1 or whatever, here're some ways.
- Ask the DM the cost, weight, and time to line the character's armor or clothing with lead. While most detect spells "can penetrate barriers, but 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood/dirt blocks [them]" (PH 219)
- Many spells conceal alignment, making the spell's target essentially detect as lacking any alignment instead of detecting an alignment. This is, obviously, suspicious. Thus the 2nd-level Clr spell undetectable alignment [abjur] (PH 297), the 3rd-level Sor/Wiz spell cloak of Khyber [illus] (City of Stormreach 59), the 3rd-level Sor/Wiz spell nondetection [illus] (PH 257), and even the 8th-level Sor/Wiz spell mind blank [abjur] (PH 253) are inferior to spells which reveal a false alignment like the 2nd-level Sor/Wiz spell misdirection [illus] (PH 254), the 2nd-level Sor/Wiz spell misrepresent alignment [illus] (RoE 188), and the 4th-level Clr spell moral façade [illus] (CC 125). Note: There exist some similar psionic powers (e.g. the 6th-level psion power aura alteration [telepathy] (XPH 78-9)).
- Magic items exist which conceal alignment. The ring of mind-shielding (DMG 232) (8,000 gp; 0 lbs.), while relatively cheap, convenient, and multipurpose, suffers the same problem as spells that conceal alignment rather than reveal a false alignment, as do many other items (e.g. less and greater Harper pins (Mag 159-60) (8,000 gp and 79,000 gp; 0 lbs.), the mask of lies (MIC 115) (4,500 gp; 1 lb.)). Undoubtedly there're items that permit an owner to reveal a false alignment rather than no alignment, but I couldn't find any.
- Some feats can conceal alignment or reveal a different alignment. The feat Mind Mask (SoS 117), in addition to other effects, reveals a creature's alignment as neutral no matter what his actual alignment, as does the feat Mask of Gentility (ElE 25) which has much stiffer prerequisites. The feat Veil of Cyric (CSW 146) conceals the evil component of the creature's alignment from lower-powered creatures.
- A Bluff skill check (DC 70) permits the creature to display a false alignment.
To conceal the character's activities, he should do everything within the confines of the 7th-level Sor/Wiz spell Mordenkainen's magnificent mansion [conj] (PH 256) or another extradimensional space (e.g. the pocket paradise created by a rod of security (DMG 236) (61,000 gp; 5 lbs.)) while under cover of the 5th-level Sor/Wiz spell Mordenkainen's private sanctum [abjur] (PH 256). Things just don't get much more secure than that in Dungeons and Dragons.
As an aside, I'm not sure if this belongs, so let me know if I'm overstepping, but
Are You Sure the Character's Truly Evil?
Evil isn't bad or unpleasant or desperate, although it can be. Evil is evil. Wanting to be immortal because of an earlier trauma isn't evil. Wanting to be immortal at all isn't evil, and, in the abstract,2 becoming immortal is as reasonable a goal for the stalwart paladin who wants to protect people forever as it is for the druid who wants to watch the seasons change endlessly as it is for the vampire necromancer who wants to plunge the world into eternal night and live there forever, feasting on the remaining, mewing blood after the sun's blotted.
In other words, while becoming a lich is one path to immortality, it certainly isn't the only one. One can use spells to gain immortality, perform rituals to do so, take classes3 that grant it--whatever. Going from, "That horrible event showed me I really don't want to die," to, "I better become an evil necromancer," is a huge leap that shows the character did little research.
And that's kind of cool. That's a valid role-playing hook. That's not evil. That's misguided. A misguided protagonist is a lot more interesting than an evil protagonist.
What the character's stepped into is pretty serious, though. Dungeons and Dragons has oodles of creatures who'd love to convince such a character that their way of living forever is the best way of living forever, and once the character's made some tentative friendly gestures their way I'd expect those creatures to come out of the woodwork and start angling for the character's feats, soul, XP, time, cash, and other resources in exchange for teeny-tiny steps along the path to what they claim is the best kind of immortality. That's very helpful to the DM who now has tons of plot all because of that character.
Further, if the character's already committed to capital-E Evil, he'll be totally okay with whatever those creature propose. Betray country, friends, loved ones, and former gods? No problem. Poison a village? Sure. Eat a whole pile of cute puppies? Whatever. Get piercings in weird places?4 Okay. For the promise of immortality, those won't be a big deal to someone already evil.
But to someone on the fence, those are real, serious choices that determine the character's fate. A willingness to do evil things to get what one wants doesn't make one evil; actually doing those things makes one evil.
If you've already written Alignment: Chaotic Evil or whatever on your character sheet and are getting mechanical alignment-specific bonuses from having done so, don't worry about all this and keep chugging along, but if you haven't and these events are all taking place during the game and the character's still on the fence, I'd urge you to keep the character on the fence. Let him make bad but not evil choices. Let him investigate evil as an option. Have him interact with some of the folks with whom he'll spend eternity. Let him make an informed choice about evil.
The Joys of Atonement
The 5th-level Clr spell atonement [abjur] (PH 201-2) is, in my opinion, sorely underrated. One of the purposes to casting the spell atonement is redemption or temptation, which reads
You may cast this spell upon a creature of an opposing alignment in order to offer it a chance to change its alignment to match yours. The prospective subject must be present for the entire casting process. Upon completion of the spell, the subject freely chooses whether it retains its original alignment or acquiesces to your offer and changes to your alignment. No duress, compulsion, or magical influence can force the subject to take advantage of the opportunity offered if it is unwilling to abandon its old alignment. This use of the spell does not work on outsiders or any creature incapable of changing its alignment naturally.
So just in case it turns out later the character made a misguided, uninformed choice, there's a way back. If more alignment wiggle room's needed consider the feat Heretic of the Faith (PF 46), and to see what the character needs to do to be redeemed, employ the Use Magic Device skill to emulate a paladin's detect evil class feature while wearing a pendant of redeption (CC 140) (8,000 gp; 0 lbs.).
- I was a player in a campaign wherein one city was ruled by paladins. The roads were fabulous. Road maintenance was the typical punishment for even minor infractions.
- Although in a specific campaign things might be different.
- Character classes... not, like, Immortality 101: Avoiding Boredom.
- Hey, it might be a thing: "Clerics affiliated with Baalzebul wear blue and black and favor gold jewelry and body piercings" (BV 159).