After having a long, heartfelt talk with my sister, I understand she wants to marry you. While I sympathized with Martha’s wish to have a family of her own, I found your whirlwind courtship and failure to open your background to scrutiny suspect.
Therefore, I did some checking on my own through a discreet private detective. He found Alan Foxglove does not exist and followed you until he unearthed your true identity. I know you to be one Albert Fox, that you have served time in prison for thievery -- stealing jewels from two other wealthy young women to be precise.
I do not want to hurt Martha with the truth. If you pursue my sister and she continues her relationship with you, I will be forced to cut off her funds immediately. If you somehow marry without my knowledge, she will not come into any money until she is thirty. I do not think a man such as yourself would be satisfied with this arrangement.
If you have even the slightest feeling for Martha, you will make whatever excuses you need to end this travesty and leave her in peace... and ignorance of your true intentions.