Setting

The Mushroom Kingdom is in a state of panic. Princess Peach, the beloved ruler, has gone missing. Mario, Luigi, and the rest of the kingdom's heroes are on a quest to find her.

If you meant an actual commercial game, double-check the title — the only official Mario Is Missing is the 1992 edutainment game (PC/SNES), which has no “Peach Untold Tale” version.

Recommendations

What is "Mario Is Missing Peach Untold Tale 3"?

First, a history lesson. The original Mario Is Missing! (1993) was an edutainment game where Luigi had to save Mario from Bowser by learning geography. It was universally panned.

Cons:

Mario is Missing 2: Peach's Untold Tale - Tales From the Internet

The "3.x" series of the game was notable for its technical polish and content depth before Nintendo's copyright interventions.

Conclusion

Protagonist: Players control Princess Peach, who is on a quest to save the Mushroom Kingdom after Bowser invades and Mario goes missing.