Can the return of my capital be guaranteed when I invest in a partnership?

I have submitted a question on a financial matter many days ago and have nkt yet reveived the reply. I am copying the question below and would be grateful for reply.

Mohamed Shafi (MS) presented a business investment opportunity to me. I was told that MS’s friend Ahmed has a real estate venture which has good profit but needs some cash to complete the full venture (which should be done in short period of time). MS told me that Ahmed (venture owner) is looking for some cash for the venture, any investor willing to give the cash as investment (for the short period of time) will get share in the profit of the venture. There was an estimated profit calculated since the venture had aready started and future sale was also almost confirmed.

I agreed since MS is also an aalim e deen. MS also told me that the money will not go anywhere, it is his guarantee and if anything goes wrong he will give me the money back from his side. Once I gave the money as investment, MS gave me some documents to sign which, to me, looked like an agreement of loan/interest. I refused to sign this document and  provided alternative agreement format to be clear from any kind of implied interest in the dealing. None of these documents were signed, however MS told me the money was already given for the real estate venture. 

After few months, MS told me that Ahmed (venture owner) had very bad accident and became mentally handicapped. MS told me that the money I gave was already given to Ahmed the venture owner and he was supposed to return the money with profit but in this meanwhile he became incapacitated due his mental instability. So recovery of my investment seemed rather difficult. However, MS was ready to return my money/investment based on the guarantee he had given to me. Is it lawful for me to take the principal investment back from MS?