I read this a long time ago...
It's probably set in season 2... there's a new serial killer in town, who attacks newly married wives, so Lois and Clark go undercover as newlyweds, staying at Clark's place. All I remember is that Clark is reluctant at first (because of danger to Lois and his Superman duties)...
Any ideas? (I'll try googling the archive with some other terms... so far hasn't worked. Meanwhile if anyone knows, Thanks in advance).