How about changing between 1st and 3rd person?

It sounds like an interesting technique. As Lorraine has said, there are many novels with changing PoVs. In some, different PoVs are always 1st person, in others, always 3rd person. To use both in the same book would create a distancing effect, the reader relating more to the 1st-person PoV.

Since you write thrillers, Clare, you might consider playing with fire and giving the 1st-person treatment to the nasty character and the 3rd-person to the more agreeable one.

Have you read Iain Banks' Complicity yet? It switches from 1st person (journalist) to SECOND person (serial killer on a moral mission) and lets you wonder for a while whether they're the same person. (I'm not saying which way the coin lands when you can stop wondering.) It's brilliant!

Judging by your earlier work, Damaged, I don't think that you'll fall into the ditch that Paula Hawkins did, of making the 2 voices too similar. You've got talent at slipping into different personae.

I'm still in Barcelona. I catch the train back in the general direction of home tomorrow morning, will reach home a day or 2 or 3 or 4 later. at which point I will collapse, catch up on some necessary sleep, detox myself from 2 cities... and get back to your Damaged ms. I'm really looking forward to it!

I've just been reading an article on the BBC website, about the new novel by Paula Hawkins, which deals with this very issue. http://www.bbc.com/news/entertainment-arts-39717279

In it, the critics complain about the sameness of the several voices which makes it hard to tell the different characters apart, even when moving from 1st to 3rd person. Worth considering if you're planning to go that route.

Lorraine