This article contains spoilers for The Time Traveler's Wife episode 1.

HBO's The Time Traveler's Wife introduces viewers to a very different form of time travel - and here's how it works. Based on the bestselling 2003 debut novel by author Audrey Niffenegger, The Time Traveler's Wife tells the story of Henry DuTamble, a time traveler whose ability is rather more of a curse than it is a blessing. At age 28, Henry learns he is destined to fall in love with and marry Clare, a woman who has encountered his future self many times.

Time travel is a theoretical science, and precious few films and TV shows really explore the concept in a consistent way - simply because they're telling stories rather than presenting a treatise in temporal mechanics. The Time Traveler's Wife is relatively unique in that it only explains its time travel in the most general terms; there's no TARDIS or DeLorean, and its stars aren't scientists who specialize in their understanding of time travel. It's easy to see why this approach drew the attention of former Doctor Who showrunner Steven Moffat, whose love for the book is displayed in his Doctor Who character River Song. He's now writer and producer for HBO's new series, The Time Traveler's Wife.

Related: The Time Traveler's Wife Cast, Character, & Changes Guide

The Time Traveler's Wife is presented as a romance, with only the lightest touch of science-fiction added as a justification for its central plot device. For all that's the case, though, it handles time travel in an unusually consistent way. Here's exactly how time travel works in this story - and what this model of time travel means for Henry and Clare.

Why Henry Can Time Travel (Ability Explained)

Time Traveler's Wife 101 Clare & Henry

The hero of The Time Traveler's Wife is Henry DuTamble, born with a rare genetic disorder giving him a unique relationship with time. The slightest degree of stress can act as a trigger to transport Henry through time - usually into the past, but occasionally into the future. He is drawn to places and events that are of great importance to his own life, as though they exert something like a gravitational pull over him. Every part of Henry's body possesses the propensity for time travel, even when dead or cut off from him; in The Time Traveler's Wife episode 1 he complains about his nail-clippings traveling through time, or a haircut that has followed him home. On the more sinister side, The Time Traveler's Wife episode 1 ends with the revelation Henry's feet will be amputated at some point, and are also jaunting through the timeline with impunity.

Whenever Henry time travels, there is the sound of air either rushing in to fill the sudden vacuum he has left behind or being displaced as he arrives. Temperature differentials are also relevant; there is a burst of steam when those feet arrive, suggesting they had been kept in a refrigerated state. Henry cannot take anything with him when he time travels, meaning he always arrives naked. This has led him to become both athletic and scrappy, because a naked man appearing in a busy street often has to run away or fight to get some clothes.

The Time Traveler’s Wife Timeline Explained

Feet the time travellers wife

The two characters in The Time Traveler's Wife have very different timelines (a plot device Steven Moffat borrowed for River Song's timeline in Doctor Who). Clare first met Henry when she was just a child, and she has grown up knowing him throughout her life. As she puts it in episode 1, there is a very real sense in which she formed herself around him. For Henry, though, his first meeting with Clare happens when he is 28 years old. From that point on, he finds himself jumping into her life at different points, particularly into the vegetation near a meadow close to her family home. Clare, meanwhile, finds future versions of Henry guiding her in her relationship with the present-day version.

Related: The Time Traveler’s Wife Must Avoid Steven Moffat's Story Problem

Why Time Traveler’s Wife Isn’t A Love Story

The Time Travelers Wife TV Series

This model of temporal mechanics essentially means The Time Traveler's Wife should not be judged as a love story at all. Love involves a choice, and in truth neither Clare nor Henry have any choice in the matter at all. This point is made clear in The Time Traveler's Wife episode 1, which shows both Clare's first encounter with Henry and Henry's with Clare. For Clare, Henry was the man she always knew she was destined to be with, and she did her best to save herself for him. For Henry, Clare is the future wife who bursts on the scene when he is 28 years old, demanding his undivided attention and singularly unimpressed when she learns he already has a girlfriend. Suffice to say this is a very different form of time travel from Back to the Future.

This is not a love story, then. Rather, because of the show's model of time travel, it should really be understood as more of a "Fate Story" - of two people who are drawn together by unique circumstances, with no freedom of choice at all. Clare forms herself around Henry, and then she reforms Henry around herself; neither has any degree of agency. This makes The Time Traveler's Wife unique in its romance, a story unlike any other.

More: Why RTD's Doctor Who Era Has Aged So Well (& Better Than Moffat's)