The Power of the Fiend (Russian: Вражья сила, Vrazhya sila) is an opera in five acts by Alexander Serov, composed during 1867-1871. The libretto is derived from a drama by Alexander Ostrovsky from 1854 entitled Live Not As You Would Like To, But As God Commands. The opera was premiered posthumously on 19 April 1871 (Old Style) at the Mariinsky Theatre in Saint Petersburg conducted by Eduard Nápravník. Among the performers were as Spiridonovna and Mikhail Sariotti as Yeryomka. Although in many ways it is more far-reaching than Serov's previous two operas, this work was not a success.