Locked in the Dark

Locked in the Dark

I'm locked behind a door alone,
My breath at rest beneath my chest;
The party jocks ignore my knocks.

Long after vain, sustained hard knocks
I sense, no more am I alone
but pressed against an ample chest!

My heartbeat thumping out my chest,
I tap out three more timid knocks;
For cause unknown, we're left alone.

Alone & blessed with treasure chest, opportunity knocks!

Tritina pattern :

3 metered tercets with rotating end words:
         A-B-C
         C-A-B
         B-C-A
Final line with all 3 words used:
         abc