Emma and Hook's love for each other is to be tested on fire in "Once Upon a Time" season 5 episode 20.

"Once Upon a Time" season 5 episode 20 is entitled "Firebird." According to Spoilers Guide, Hades is set to turn to the heroes and seek for their help with having Zelena back from Peter Pan and Rumplestiltskin. The god of the Underworld will tell them them that he will erase their names from their tombstones in exchange.

As per the publication, Hook still cannot leave the Underworld, which leads Emma to join the former on a journey in the deep kingdom of Hades. Flashbacks will also see Emma look for answers to the questions about her family. In fact, she is set to make an unforeseen friendship, but exact details on the who and how are yet to be revealed. In line with the locale, Cruella De Vil is also eager to keep the trapped heroes in "Firebird."

Previously, Regina asked Cora to help her with Zelena in "Once Upon a Time" season 5 episode 19. Entitled "Sisters," the episode revealed that Hades and Zelena were united once again, with the former telling the latter that he was interested on having their future outside the Underword.

According to Spoilers Guide, Zelena had to heal Hades' heart with "True Love's Kiss" for them to be able to leave the Underworld and trap the heroes for good. Regina overheard Hades and Zelena's plan, so she asked Cora's help to generate a plan that would lead to Hades and Zelena's separation. As per the publication, Cora also revealed a family secret that could impact Regina and Zelena's lives.

"Once Upon a Time" season 5 episode 19, "Sisters," aired on Apr. 24 while episode 20, "Firebird," airs on May 1.