Spies in St. Petersburg

Book 1 of 4 in the Taylor & Rose Secret Agents series.
"With Sophie still missing in action after their explosive mission in Paris, Lil decides to take matters into her own hands. On a new mission for the Secret Service Bureau, can Lil find Sophie in misty, mysterious St Petersburg? Can they uncover the identity of their true enemy and can they trust anyone – even the Bureau? It's time for Sophie and Lil to put their spy skills to the test."