How does the author present "grief" as one of the novel's main themes?

Grief is a central theme to the novel, as seen through the main character, Nat. Nat is an orphan who is being raised by his aunt. Nat's mother died of cancer, and shortly after, his father commits suicide out of grief. Nat finds his father's body lying in a pool of blood, and has the image permanently ingrained in his memory. Left parentless, he moves in with his aunt. Nat and his aunt do not discuss the death of his parents, denying Nat the ability to grieve and move forward. At the recommendation of his aunt, Nat begins to act in community plays as a distraction from his sadness. Nat quickly takes to acting, and excels in the theatre. With acting as a distraction, Nat further distances himself from the grieving process.

When Nat joins the Company of Boys, his new friends ask about his parents. Nat is unwilling to address their deaths, and lets his emotions continue to fester without fully acknowledging them. When Nat is transported back to 1599, he finds a father figure in William Shakespeare, and with this newfound comfort, some of his emotions come rushing to the surface. Nat tells Shakespeare of his troubled past, and with Shakespeare's support, is able to begin the grieving process.

When Nat is transported back to the present in 1999, he suffers another devastating loss, this time losing Shakespeare as a surrogate parent. Nat is heartbroken by this newest loss, and cannot contain his emotions internally anymore. He has several arguments with Arby, the director of the Company of Boys, over the integrity of his production of A Midsummer Night's Dream, and ultimately loses control of his emotions altogether. When Arby explains to Nat the significance of his journey back to 1599, Nat is finally in a position grieve the losses he has suffered and move forward.