The situation with Supergirl’s squeeze is up in the air, so to speak, when her TV show returns to the CW Monday at 8 p.m. ET.

“There are lots of questions,” says Chris Wood, who plays Mon-El, better known on Earth as Mike, as Supergirl launches its third season. “Where is he? Where has he been? Can we find him? Is he ever coming back?”

In real life, as it happens, Wood and Melissa Benoist, who plays Supergirl, have joined forces to promote IDONTMIND, Wood’s mental health awareness campaign.

But on-screen the whereabouts mystery may linger for a while. “I think we’ll tease it out at first,” Wood says.

That pumps up the stress level for Supergirl, Earth name Kara, as she gets deeper into her career as a writer. She also must navigate minidramas from a couple of worlds while doing her part to save her adopted planet. Does she really also need Mon-El to go walkabout?

Wood, who joined the show in Season 2, says he came in with “a basic outline of last year and the setup for this season. But it always surprises us when we get a new script. It’s usually not the way you envisioned it in your mind.”

Joining a show in its second season can be a challenge and Wood admits that “if you asked me about that a year ago, I would have said it takes a while to find your dynamic in the ensemble.

“You don’t want to throw off what they’ve built. But the whole cast was very welcoming. Now, honestly, it’s hard for me not to feel like I was a part of it from the beginning.”

The 29-year-old Wood is practically a member of the CW repertory company, having previously been seen in The Vampire Diaries, The Carrie Diaries, and Containment.

He branched out to PBS with a role in the lamentably concluded Mercy Street, and he notes that his original acting training was in the theater and musical theater.

“I lived in New York for six years and did a couple of pre-Broadway runs,” he says. “Then just before they moved to Broadway, I got a job in L.A. So you could say I almost made it there.”

He laughs.

“Live theater,” he adds “is definitely something I’d like to get back to.”

Meanwhile, he has plunged into IDONTMIND, which he describes as a “deeply personal” project whose goal is to destigmatize mental illness.

Wood’s father died after a frustrating battle with what Wood now says was an undiagnosed and then inadequately treated mental illness. He says he has struggled himself with symptoms of ADHD and OCD.

“I didn’t start to get better until I started talking about it,” he says. “That’s the best prescription you can write for yourself.”

That’s why a major part of the IDONTMIND program is facilitating a worldwide conversation on social media, where people can share the pictures, stories, thoughts, and courses of action.

“The response has been terrific,” says Wood, who further notes that this sort of discussion “is not what our social media is usually about. It’s usually about the best stuff, how we live perfect lives.”

But using social media to discuss challenges, he says, “is also very positive and encouraging. To talk about this isn’t a sign of weakness. It’s a sign of strength.”

IDONTMIND’s first campaign includes Benoist and features hats and T-shirts, which Wood says help spark more conversation.

“Kids pay more attention to their clothing than their mental health,” he says, only half-joking.

Working with other mental health organizations while keeping his own group’s focus on removing the stigma around mental illness, Wood says his personal goal is for IDONTMIND to reach the point “where I can remove myself.... I’m uncomfortable using my platform [as a celebrity] to promote something.

“But I didn’t act for a long time because I was hoping someone else would do it. I finally realized if I wanted it to happen, I needed to be the one.”