You've been found out with 〜てんだ

Grammar Explanation: Contracting 〜ているのだ to 〜てんだ

Shin’ichi reveals that the murderer escaped out the window and onto the roof, naming the wheelchair-bound husband as the culprit. The husband points his cast-covered leg, but Shin-ichi knows better.

新一(しんいち):: 「もう、ネタはバレてんだ！！」; “Your deceit has already been found out!”
メイド:: 「だ、だんな様(さま)、足(あし)が…」; “Master, your leg...”

Key Points

1バレてんだ = バレているのだ

〜てんだ is a spoken contraction of 〜ているのだ.
Here バレてんだ means “it has been found out” or “the trick is exposed”.

2んだ adds explanatory force

Rather than just stating a fact, Shin’ichi is forcefully declaring the situation.
That explanatory んだ gives the line a decisive “I’m telling you, it’s over” feel.

3もう marks that it is already too late

もう signals that the exposure has already happened.