You could do Trail of Cthulhu (Pelgrane Press), using the Pulp Rules option.
It's a superb book. If you want to get a feel for how the GUMSHOE rules work, 5 minutes of reading here shows them in use in a Night's Black Agents (super-spy) game. Note quite the same, but pretty close.After reading a few reviews of this I ordered a copy. While it might be too investigative for my initial plan I may like that enough to keep it, too. Otherwise this seems to offer a lot of what I needed, and the stability rules take care of my issue with sanity (too easy to lose it)
Thanks!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.