Between Bel's two fires. Scylla on one side and Charybdis on the other. In Irish, Itter dha teine Bheil, in a dilemma. The reference is to the two fires kindled on May Eve in every village, between which all men and beasts devoted to sacrifice were compelled to pass.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894