Citation: 4A_80/2013 E. A

X.________ (Klägerin, Beschwerdeführerin) war ab Januar 2000 bei A.________ Ltd., London, als Executive Director in der Personalvermittlung angestellt. Sie gab diese Stelle bereits Ende Februar 2000 wieder auf. Im Februar und März 2000 führte sie Gespräche über eine Zusammenarbeit mit B.________. Dieser war damals Managing Director und European Representative der C.________ Group und - nachdem diese Investorengruppe zusammen mit Mitinvestoren 1999 den Y.________ Konzern übernommen hatte - seit November 1999 Verwaltungsratspräsident der Y.________ AG (Beklagte, Beschwerdegegnerin). Am 24. März 2000 verfasste B.________ auf Briefpapier der C.________ Group folgendes Schreiben an die Beschwerdeführerin: "Dear X.________, Further to our conversations regarding the terms of your engagement as Assistant to the Chairman of Y.________, I am pleased to propose the following terms. Position: Assistant to the Chairman of Y.________ (the «Company»). Based in Brussels with offices in Brussels at the office of D.________ and in London at the headquarters of the C.________ Group Europe, Ltd. Sign-up Bonus: $ 50,000 Basic salary: $ 300,000, paid in 12 equal monthly installments. Basic Salary will be increased by 10 % annually. Annual Bonus: 50-150 % of Basic Salary, based upon performance. Share of value creation: - Option on .5% of the Company's shares («Options»), exercisable at a price per Company share equal to C.________ Group's buy-in price per Company share. - Options vest on the following schedule: 20 % upon signing of a definitive agreement; 20 % upon 12 months continuous service; 20 % upon 24 months continuous service; 20 % upon 36 months continuous service; and 20 % upon 48 months continuous service. - Options will be granted by the Company under its incentive stock option plan for senior management and consultants. The number of options granted will be reviewed and may be increased after 24 months continuous service. Duration: The Agreement will be for a four-year term, with a start date of July 10, 2000. Part-time work before the start date will be compensated at a daily rate based on the Basic Salary. Miscellaneous: - Structure of agreement (e.g., consultancy or employment) to be mutually agreed. Payment entity to be determined. - Assistant to be based in London and right to hire a business analyst to be based in Brussels, London or Switzerland. - Three months paid maternity leave (to be counted for purposes of option vesting and bonus). - Insurances: Health, Dental, Life and Disability at substantially the same level of current coverage. - Four weeks of holidays. - Reimbursement annually for tax, accounting or estate planning expenses. - Reimbursement for work-related expenses, including child care and travel expenses as required. Position: Assistant to the Chairman of Y.________ (the «Company»). Based in Brussels with offices in Brussels at the office of D.________ and in London at the headquarters of the C.________ Group Europe, Ltd. Sign-up Bonus: $ 50,000 Basic salary: $ 300,000, paid in 12 equal monthly installments. Basic Salary will be increased by 10 % annually. Annual Bonus: 50-150 % of Basic Salary, based upon performance. Share of value creation: - Option on .5% of the Company's shares («Options»), exercisable at a price per Company share equal to C.________ Group's buy-in price per Company share. - Options vest on the following schedule: 20 % upon signing of a definitive agreement; 20 % upon 12 months continuous service; 20 % upon 24 months continuous service; 20 % upon 36 months continuous service; and 20 % upon 48 months continuous service. - Options will be granted by the Company under its incentive stock option plan for senior management and consultants. The number of options granted will be reviewed and may be increased after 24 months continuous service. Duration: The Agreement will be for a four-year term, with a start date of July 10, 2000. Part-time work before the start date will be compensated at a daily rate based on the Basic Salary. Miscellaneous: - Structure of agreement (e.g., consultancy or employment) to be mutually agreed. Payment entity to be determined. - Assistant to be based in London and right to hire a business analyst to be based in Brussels, London or Switzerland. - Three months paid maternity leave (to be counted for purposes of option vesting and bonus). - Insurances: Health, Dental, Life and Disability at substantially the same level of current coverage. - Four weeks of holidays. - Reimbursement annually for tax, accounting or estate planning expenses. - Reimbursement for work-related expenses, including child care and travel expenses as required. If you accept this offer, I will instruct Y.________ management to prepare final documentation for your review immediately. In consultation with Y.________'s Belgian and U.K. legal advisors, we will work together to structure your relationship with the company in the most efficient manner possible. I trust that you will share my enthusiasm over the opportunity to participate in Y.________'s success, and I look forward to working with you. Sincerely, B.________ Chairman of the Board, Y.________ Acceptet and agreed to: X.________" Die Beschwerdeführerin unterzeichnete diesen Brief und nahm in der Folge die darin beschriebene Teilzeittätigkeit auf. Die beidseits beigezogenen Anwälte arbeiteten mehrere detaillierte Vertragsentwürfe aus. B.________ eröffnete der Beschwerdeführerin indes am 23. Juni 2000, dass er die Zusammenarbeit beenden wolle, was er am 7. Juli 2000 schriftlich bestätigte.