Based on derpi image #1763117 (NSFW) - posted with permission from the artist. Cover art is a snip from the same image. Credit to Lunargue for its creation!

Captured by the Sirens, most of the mane 6 are helpless under the sirens' lustful touch, the emotion-eating predators intending on using their sexual energies to repair their hearts. The girls' only hope lies in Twilight and Sunset, who were away when the Sirens captured them.

At gunpoint, and helpless against the superhuman strength of their captors, one thing is for sure; if the two can't do anything, their friends' fates are sealed...