Code Name: Aggie~By Way of Introduction

Of all the central characters on the series,  Poirot,  Felicity Lemon was the only one who hadn't endured any physical hardship.  A heartache or two but nothing by way of a serious illness.  And there was the key.  How do I get Poirot relentlessly involved in a case, to where he is not only determined for justice, as he's known to be,  but personally determined to find the criminal?
Needless to say,  Hastings,  Japp and Poirot  get their bad guys, but NOT without consequences.   After all, money's involved, and what's a human life compared to hundreds of thousands of pounds (or MORE!)  . Besides, Hercule Poirot et ensemble stepped on some very powerful feet.

   To what lengths would the minds, attached to those powerful feet, go in order to vanquish the man who brought down a very lucrative operation?