M&As are fraught with dangers of failure. Failures may happen due to misjudgments and mistakes in any of the phases of an M&A process. Over-estimation of Synergy evaluation is cited as one of the most frequent reasons for value destruction in M&A. This paper studies the M&A process of a multi-business company, with particular focus on its Synergy evaluation phase. The presented case follows an actual acquisition bid made by the company. The case-study adopts an explorative approach with data collected through participant-observation and interviews conducted during the course of Synergy evaluation. The paper proposes that big multi-business companies need to be extra careful in selecting their acquisition targets as they may face hidden dangers lurking behind the façade of attractive synergy justifications because an acquisition may have an unforeseen effect on other divisions within the company. This can be prevented as long as these companies do a thorough synergy evaluation and follow well-laid out M&A processes as analyzed in the presented case. Further, the paper also proposes to split the step of Synergy evaluation into analyzing positive synergies and negative synergies and proposes further research into systematically enumerating factors of dis-synergy in various situations of M&A for benefit of future acquisition managers.