。
Uncover the mystery hidden behind the murder case.
Literal
Murder-case [genitive-の] back-side [target-に] hide-lurk mystery [object-を] solve-clarify [imperative-せ].
Dramatic writing, sounds like a game or novel subtitle. 潜む ('to lurk, lie hidden') attached to 背後に gives a sinister, cinematic feel. 解き明かす is a compound verb meaning 'to solve and reveal' — the 解く stem ('solve') plus 明かす ('reveal, disclose'). The final 解き明かせ is the bare imperative form — direct and authoritative, typical of commands or dramatic exhortations.