It's a tale of two cities, or in this case two relationships, for "Grey's Anatomy" season 12 since couples Owen and Amelia and Kyle and Stephanie will find themselves at a crossroads. And their respective decisions could change their lives forever.

Meanwhile, Callie and Arizona's troubles are spilling over into the workplace, which puts their friends in an awkward position to take sides.

According to the "Grey's Anatomy" episode 21 preview by TV Fanatic, Callie and Arizona are trying to persuade their co-workers into becoming character witnesses in the ongoing custody battle.

"Karev, with his position as chief of pediatrics, would be great to have in your corner, and Arizona was his mentor," it said. "But Meredith is a mother, which surely would weigh well with a judge, and has been close with Callie since George died."

The official synopsis for episode 21 of "Grey's Anatomy" season 12 reads:

"Stephanie's relationship to Kyle becomes complicated. Meanwhile, Meredith encourages Amelia and Owen to take a chance and choose to be a real couple. Arizona and Callie are at odds and put their friends in the middle of an uncomfortable situation."

The series has always been very good about exploring relationships amid the stressful hospital environment. Episode 21 should be interesting since it will tackle love, but also the aftermath if relationships fail.

"Grey's Anatomy" season 12, episode 21 airs on Thursday on ABC. Watch out for more previews of the popular series which will be published here when they become available.