When Castle learned that Alexis was not only working but actually solving cases, he officially hired her to work for him.Upon the successful resolution of a case, father and daughter shared a 50-year-old scotch and cigar-blowing-bubbles.In season six, she returns from Costa Rica with a boyfriend named Pi, and the two move in together some time later.After a couple episodes Alexis realizes that Pi is not the one for her and eventually breaks up with him.In season five, Alexis finally chooses to attend Columbia University so as to remain close to family and friends, and lives in their halls of residence while frequently dropping into her father's loft.She is kidnapped by an ex-KGB officer who previously crossed swords with her mysterious grandfather, but displays her father's resilience, deductive logic and skills during the encounter.
Alexis begins dating a boy named Ashley in season three.
Working alongside Beckett gives Castle a new source of inspiration and, after assisting Beckett with the case, Castle takes the opportunity to use his knowledge and skills, and his close friendship with the Mayor, to stay on with the NYPD in a consulting capacity.
Captain Katherine "Kate" Houghton Beckett (Stana Katic) is a homicide detective with the NYPD.
They hope to attend Stanford University together, but while Ashley gains admittance, Alexis fails in her attempt to apply for early admittance, which distresses her greatly.
Though they attempt to carry on a long distance relationship, the strain of doing so is too much, and Alexis breaks up with Ashley in season four.