LONDON: When utilized correctly, a surprise twist can turn a good movie into a great one — see the early work of M. Night Shyamalan, for example. But when the big reveal lacks the substance behind it to keep the movie’s momentum going, it can lead to an overwhelming sense of disappointment — see some of the later work of M. Night Shyamalan, for example. Unfortunately, “Encounter” — directed by Michael Pearce (responsible for 2017’s excellent “Beast”) and released on Amazon Prime — falls firmly into the latter camp. The sci-fi thriller stars Riz Ahmed - who was nominated for an Oscar in 2021 for his performance in “Sound of Metal” - as Malik Khan, a former US Marine who, we learn during an excellent first 20 minutes, is involved in a battle against an invasive extra-terrestrial microorganism which turns normal people into unwilling hosts. When Malik’s ex-wife is bitten by an alien insect, he snatches up his two sons Jay and Bobby, and heads out on a road trip to safety. To say too much more would give away the movie’s central concept, but suffice to say all is not what it seems. Sadly, the grand twist that Pearce drops in surprisingly early will leave audiences hankering for the pre-reveal part of the movie. Ahmed, to his credit, turns in the kind of heavyweight performance we’ve come to expect from him. He paints Malik as an embattled soul, torn between his sense of duty and his love for his family. He is a man haunted by PTSD, frantic with worry for his sons, and increasingly running out of places to run. The movie’s second half feels overly stretched — stripped of its gravitas by the narrative shift and lumbering to a standstill following the loss of momentum. In places, this is an affecting, powerful story of paternal love in the face of a terrifying, largely unseen, threat. But more often than not, it’s a movie that’s not as clever as it seems to think it is.