Although not part of an official trilogy, the episode serves as a prelude to the impending demise of the Tenth Doctor in subsequent episodes that conclude series four. In doing so, the episode explores the Doctor’s inner demons, exposing his primal fear and arrogance; his song is ending and he defiantly refuses to accept the dictum. Arriving on Mars, he encounters the historic but ill-fated colony of Bowie Base One. The episode embodies the bittersweet motif that is
woven throughout the rebooted series. Awed by the crews’ significant contribution to human history while saddened by the knowledge of their inescapable tragedy; the Doctor’s hands are bound by the fixed moment in time that irrevocable moment necessary for the future to be extant. Tacitly accepting that the crews’ fate is necessary to maintain the integrity of the historic timeline, the Doctor initially refuses to intervene. 
Yet ironically, he reverses his nonintervention stance, motivated perhaps by his own desire to survive and driven by the darker impulses of the Time Lord Victorius. The Doctor’s manic exuberance is subverted by Captain Adelaide Brooke, who serves as his foil; her suicide ends his arrogant moment.  The fear in the Doctor’s eyes, the haunting image of Ood Sigma and the crescendo of the Doctor’s song beautifully coalesce to depict his undoing… he’s gone too far.