在失物招领处工作的巡查部长天树悠（东山纪之 饰）根本没有前往现场的机会，绝大多数时候都跟各种遗失物品打交道，偶尔接待一下前来参观的小学生还要被烦的不行。不过这并不代表他是个没有什么能力且无足轻重的小警察，他对细节的敏锐观察力和推断能力证明他那休眠许久的警魂仍未老去。某天，在协助临场警察解决了一起家庭主妇自杀案后，他被担任警视厅搜查一课12系系长的片冈正敏（吉田钢太郎 饰）召到自己麾下。虽然贵为搜查一课，但是12系仿佛一个不受人待见的边缘所在，有能力和抱负的刑警先后离开，如今这里仅有沙村康介（高岛政宏 饰）、山下巧（片冈爱之助 饰）、永泽圭太（铃木浩介 饰）、水田环（仓科加奈 饰）等个性十足又没什么干劲的刑警。
天树的到来，似乎终于改变了12系尴尬的局面……

A being of light hailing from a faraway galaxy unites with Yuma, the protagonist who owns tremendous “power of imagination,” and they form the gigantic new Ultra Hero: Ultraman Arc.

The meteorite believed to have once killed off the dinosaurs actually rattled the Earth into two parallel universes — Another Earth and Dino Earth, where dinosaurs continued to thrive. Now they have evolved into the Saurians, a race of humanoid dinosaurs, and the Bakuryu , a race of mechanized dinosaurs. But the wall between our universes has been breached. The Evolians that have been at war with the Saurians and Bakuryu have invaded, and it's up to the Abarangers to protect the world!

A mysterious space sage entrusts Yuma with challenges that surpass the limits of his imagination with a stake too high. He asks, "Should you fail… then you… will lose your power as Arc." The burden of protecting Hoshimoto City alongside SKIP members are twisted by Sascal, who manipulates them, sending challenge after challenge toward Yuma. Battling giant kaiju, an evil alien bent on destruction, and a warped dimension where even time itself is distorted, Yuma must confront the ultimate test. Will he... will Ultraman Arc overcome the greatest challenge yet and protect the future, surpassing the limits of the power of imagination?