。
Calm down.
Literal
Calm-down-[imperative] [emphasis-よ].
Note the partial-kana spelling 落ちつけ, where 着 is rendered in kana — this softens the visual register slightly compared to the all-kanji 落ち着け. The plain imperative + よ remains the standard casual 'calm down' command, often softened or harshened by intonation alone.