If it's a happy one, then the transition stage is really about you learning the new environment, the direction and pace of desired growth of the firm/practice, any new performance management or progression structures in place, the capability of your new peers, etc. Ask yourself if this acquisition will open up new opportunities for you or confine you? Most likely your Partners saw it as a great opportunity to expand.If the new environment fits your ambitions. Then start building relationships, understand how to navigate the progression structures and as BEP said, jostle for position and build that profile. You're the new kid to the block, but with a fancy new toy that everyone wants to see. Use it to your advantage.