The question to ask yourself is: if everyone involved knew what was going on, how would you expect them to feel?- If you started with the company in September and decided to stay with them, but they found out you had signed elsewhere and they were (in effect) 'on probation' would you feel embarrassed?- If you decided to leave that company and join the other company in November and they found out that you'd signed for two companies and worked for a competitor after signing their contract, how would they feel?I think the answer in both cases is probably that they'd be p*ssed off. I'm not saying you would necessarily get found out but (a) you might and (b) if you are interested in the 'ethical decision' then getting found out shouldn't matter.My advice would be to make your mind up and gracefully bow out of one of the contracts.