That is, I believe, the whole point of this situation - to put you in the position of having to choose between lying, a sin, and protecing innocent life. I could make lots of comments on this concept, but I am interested in seeing how others might deal with these situations and see what reasons they give for their choices, especially if they can find strong scriptural support for those the choices they make. I don't want to poison the well here, with my thinking.
Here's my confusion. An act is not sin, necessarily, but sin is more of an inclination of the heart and/or will away from God's plan. Would protecting an innocent life be a sin?
The danger of course lies in the slippery slope of justifying lying or other behaviors as somehow fitting into God's plan when it's more of twisting one's own agenda into one we can convince ourselves is God's. But setting up hypotheticals is usually a recipe for trolling for dissention.