Just open Cortana and ask her "Surprise Me!" she will present you with a riddle. This feature was out earlier last month with a mirror image as riddle.
And today it looks like another riddle is out for you to solve.
It states:
First in action
First in line
First in aid and
All align
If you think you got the answer for it just tap 'Solved it? Tweet it!' button
Pretty cool challenge ha?